Wow, Abraham. What can I say? THANK YOU. I really appreciate you taking the time to do that.
The King's Gambit bad for amateurs?

It's only good for amateurs. It scores pretty well below master level. As you climb thechartsit scores less well until it's no longer used. There are very few openings even us amateurs can't venture XD

I am just wondering if the King's Gambit is perhaps not the best choice for weaker players. Unlike the Queen's Gambit (which I've done well with), I have never done well with the King's Gambit, and neither have my opponents.
I was reminded of this recently with two games of mine where my opponent loses immediately. For me the key is giving back the pawn for a massive lead in development, and then just blitzkrieg the opponent.
Something tells me that the King's Gambit is probably left for chess players that know what they are doing. Class C players such as myself are probably better served using other openings, but I am wondering how others in the Chess.com community have faired using it and facing it.
It's risky (and perhaps slightly dubious), but it isn't bad. In the King's Gambit Accepted, Black can give back the pawn in order to gain valuable time for developmet. To put it simply, Black can equalize.

But but but pfren Morphy and knight odds and checkmate ends the game.
Actually, what you just reminds me of something I recently read about Tal. Many of his sacrifices lead to really imbalanced endgames that favored him. It just wasn't the mates that his opponents were scared of.
The KG can be tricky for both sides.
Yesterday I made a post about 'studying openings is UNDERrated', and my experience as white with the KG is exactly what your post gets at. White makes reasonable-looking moves in OP's games, and still gets blown off the board from start to finish, king breezing in the wind. Sure, there are improvements as recommended above, but they are not failsafe solutions to the tricky positions that result.
I recently got John Shaw's "Kings Gambit" Grandmaster guide book, and he recommends the "Quaade" line with Nc3! in response to black's h4 (in the OP's posted games, white uses FIscher's N retreat, which is playable but can be super tricky OTB.) It's an excellent reply, and something that even GMs have neglected to analyze until his book. There is pretty much nearly zero way you'd find these moves and the plan behind them over the board, even though they're not that complex - they're just not naturally played moves by white, and even GM Shaw says they're really tricky for either side to play but white can get a big advantage if he knows the plan.
I really think playing either side of the Kings Gambit is a very good illustration of the importance of having to study specific lines in openings. For example, if black doesn't know in the FIscher Defense to push g5 after d6, he often gets a very inferior game, but both d6 and g5 as black were nonintuitive enough that FIscher had to prove it in play before it started being widely used.
If you don't study the lines in the KG, and just try to 'play be general principles', there's a good chance you'll get into some really horrible position even against a weaker player. (There are a lot of white lines where the very natural looking Bc4 leads to such bad positions even if it doesn't immediately lose - Shaw shows quite a few of these in his book - it's not as simple as understanding a general principle to understand why Bc4 is bad.)
I'd probably call them less mistakes as opposed to preferences in play. He even admits that some of his lines are evaluate as objectively better for black with perfect play, but he prefers lines where chances of going wrong are much higher for black, even if with objectively perfect play, black has the advantage.
In either case, I don't need anything even close to perfect for opening analysis and repertoire - I just need something that deals with the most demanding lines and gives a lively and fair game with good attacking chances. In the KG, if you don't study the opening, there's a good chances you'll get outright lost positions even if you haven't objectively violated any cardinal opening rules in chess. (That confounded me for quite awhile in the KG - I 'did everything right' and still got a losing position.)
Also regarding ..d6, you cannot deny that even if Fischer didn't play it as black, his analysis was the main force in driving it into a main choice as black in response to the KG, even if there are good responses now (as Shaw points out.)
Also, I honestly haven't gotten to Chapter 15 with Shaw's Nc3 refutation of Bc4, but from just browsing it, it's almost certain that he seriously considered the 3..d5 response you said he overlooked - it looks like the 2nd game in that chapter Game 48 has that move, just delayed to 5..d5, so it's likely an early transposition. Even in the opening of the chapter he directly says "Black's third move (Nc3) works so well...because black can either defend his extra pawn with g7-g5 or counterattack with ..f6 followed by d7-d5." I seriously doubt he failed to consider 3..d5.
I get mixed results with the king's gambit. I've lost the last few unfortunately, but it has not scared me off the opening. I like it a lot in fact as the resulting positions tend to be quite sharp and the games fairly intense.
3. d6 for black is a good move and one I consider, but doesn't scare me off. I simply go towards a Quaade style game and instead of countering g5 with h4, i play g3.
That said, it seems that plenty of players at my level forget that g5 is supposed to follow d6 and they often play Bg4 to pin the knight, which I'm totally okay with.
I will continue to play the KG to work out kinks because I enjoy the sharp open games. Shaw's book has been a big help as well in knowing white's plans in the KG if not what move counters what move.
I never get the chance to play against the KG as black however as I'm a pretty loyal sicilian player, with an occasional french. I avoid e5 like the plague.
I love those g3 lines as white. g3 as a later response to h4 is barely even mentioned in most KG opening resources I've seen (FCO, youtube KG summaries, etc.) so right there you can have an advantage against less prepared opponents, as the kind of play that ensues aren't types of situations for black that 'play themselves' (with obvious strong moves.)
And the best part is that Shaw considers it a 'best line' - it's not like you're seeking out some dodgy sideline just to confuse the opponent and end up playing a weaker line.
Yeah, most lower rated players (like me) seem confused when they see this. They often take on g3 instead of pushing g4 to threaten the knight and then f3, which I think is the stronger continuation. Taking on g3 just opens the h-file for the rook and exposes their g5 pawn, while allowing white to keep a pawn on g3 as support for their knight to move to h5 with now double defense as the rook is lined up there too.

I am just wondering if the King's Gambit is perhaps not the best choice for weaker players. Unlike the Queen's Gambit (which I've done well with), I have never done well with the King's Gambit, and neither have my opponents.
"Perhaps not the best choice" is a pretty low bar, which could perhaps be said for any opening.
"I have never done well with the King's Gambit, and neither have my opponents" is a pretty small sample.
FWIW, the Slow Chess League database currently shows White managing 72.5% on the basis of 63 games -- which makes the King's Gambit about the highest scoring opening in League play for White.
(The Slow Chess League is group that originated on chess.com in which players make formal appointments to play games online at slow time controls.)
Sixty-three games isn't a huge number either, but it does suggest that the King's Gambit is quite playable at the amateur level, though it may not be everyone's cup of tea.

I had a couple of college friends who played the King's Gambit all the way up to 2200. Some of their victories made it into the big online databases.
The King's Gambit suited their style and tournament strategy. They had limited time for opening study, they were strong tactically, and they were very aggressive, competitive players.
Not everyone is wired that way. But if you are happy to throw a hand grenade onto the table and see who comes out alive, the King's Gambit is a good choice.

If you are happy to throw a hand grenade onto the table and see who comes out alive, the King's Gambit is a good choice.
You hit the nail on the head with that description :)
Rosenbalm, in general it is believed to be good for amateurs to start with open tactical openings in the beginning of their chess careers since this will force them to calculate lots of lines, making them improve their calculation. The King's Gambit seems perfect for this. You should of course study all aspects of chess and eventually chose openings that fit your style but calculation is the number one thing holding lower rated players back.
I'm not an advanced player, but now that I've been studying the KG, I really would NOT recommend it for beginners. It's simply too easy as white to get blown off the board wholesale after one small mistake, which is why it's so important to study specific lines in it.
Also, beginners often learn the italian game setup with Bc4 move thrown in, and in many KG lines, Bc4 is a bad move (yep, I learned this the hard way too, lost a lot of games not even knowing why until I saw that I was playing a line Shaw considers pretty much lost for white, but looks easy on the eyes as white.)
Furthermore, the KG has totally bizarro world setups in the opening that don't look logical at all, and don't have much to do with the typical 'beginner rules of opening' chess. I'm finding you have to throw a lot of those beginner opening rules out the window in the KG and learn the specific lines. If there's one thing beginners have to get down, it's king safety, and in most of the KG lines, white's king is not under full castle protection and might even be in the middle of the board even in an open position with multiple black pieces nearby!
I think most beginners at white would get crushed very quickly with the weakness around the king. The Cunningham defense by black (black plays early Be7, then goes for the immediate Bh4+ to force white to play Kf1 and stop castling) is often lethal against beginners who have no idea how to defend, even though it's a good line for white if you know what you're doing and counterattack in the middle forcefully. I get a kick out of people using that attack on me now when I gleefully play Kf1 and execute my central control setup, but that Kf1 move used to be the sole reason I feared playing the KG as a beginner who didn't study the opening and tried to figure out everything OTB.

Yeah. I don't see why those who go on about the wonders of open games and tactical openings for newish players don't recommend the King's Gambit. Being a pawn up or down doesn't matter much for a long time in the early stages.
I also have a theory that the KG is a good weapon against mid-level class players who are used to playing safe, sensible chess, but may not be able to handle chaotic positions.
That seemed to be working theory for one of my friends. He would play some offbeat line, wind up the tension, then lunge at some poor class player like a wolverine. It wasn't pretty, but it often worked.
Not that everyone should play the King's Gambit, of course.

Furthermore, the KG has totally bizarro world setups in the opening that don't look logical at all, and don't have much to do with the typical 'beginner rules of opening' chess.
hnnng1: That's not a bug; it's a feature!
Otherwise your points are well-put.

I have friends rated 2000-2350 who play the King's Gambit as part of their repertoire. It's fine for "amateurs". It's not so fine for professionals or for competitive correspondence players.
Those who really want to play the KG in correspondence probably need to buy Shaw's book and analyze it to death.
I am just wondering if the King's Gambit is perhaps not the best choice for weaker players. Unlike the Queen's Gambit (which I've done well with), I have never done well with the King's Gambit, and neither have my opponents.
I was reminded of this recently with two games of mine where my opponent loses immediately. For me the key is giving back the pawn for a massive lead in development, and then just blitzkrieg the opponent.
Something tells me that the King's Gambit is probably left for chess players that know what they are doing. Class C players such as myself are probably better served using other openings, but I am wondering how others in the Chess.com community have faired using it and facing it.