2...d5?? 3. Qh5+ +-
of course first Nf6 and than d5
(I probably shouldn't be bothering to take this bait, but) White gets to play has a move in between there too.
After Nf6 White can play d4 and it does seem, like you said d5 is necessary for Black to get any play at all so d5 Bd3. White is still up a pawn, and now Black will have to play "around" the large hole in front of the backward pawn in the middle of the board, or play e6 making the gambit permanent... so no recapture. And ok Black isn't much worse in the center after that exchange and can hope to attack down the f-file. Playing chess "Without counting the pawns" might work a bit in Blitz, but Black can have this sort of thing from other openings without giving up a pawn to do it.
Also after Nf3 White can get tricky with Be2, also just about every plan that works against the King's Gambit works better up a tempo against the Fred. In the KG White has a strong pawn on e4. Paraphrasing many others, in the Fred Black has no pawn on e5 and isn't likely to get one there any time soon. It's not a good move. It probably is the worst thing on the board in that position.
Moreover, Fritz13 gives for 1.e4 f5 +- 1.29
and for 1.e4 b5 +-1.67 (after 30 seconds)
Fritz? Who the heck uses that when there's Houdini 1.5a/2.0/3.0 . . .
I can picture someone wading through the forums looking for these, "what's the best black response to 1.e4 and what's the best white response to 1...e5" threads assembling their frankenstein repetoire. "Today, Chess.com. Tomorrow the world!"
I want to tell them, "You don't have to send your move through the mail on a postcard anymore. Use the game explorer of masters' games and databases!!"
Thanks for letting me get that out of my system and I trust it was at least thought provoking even if you didn't happen to agree.