Center/Scotch game e4 e5 d4 exd4 Nf3

Hey, I was wondering if anyone here could explain to me what's the downside of achieving the Scotch through the center game move order.

Of course, I understand that Black doesn't have to play Nc6, and has some other options, but which one of them is particularly good? It seems like someone who plays the Scotch can either avoid the Petrov and maybe even Philidor (relatively major openings) or some random center game lines. It seems like an no-brainer, unless of course some these are somehow critical, does anyone here know?

Well I would say there are additional options for black this way. How are you meeting 3.c5 if black trys to hold the extra pawn? A lot of murky lines with 4.Bc4 or 4.c3 maybe, would need checking. Also 3.Bb4+ looks a bit annoying. 

I play that almost all the time. I am a poor player but I am very experienced in those positions. I like it because at my level it give so many opportunities to black to pick poor moves. Also it is very flexible.  After 3.nf3 there’s a ton of common positions and also independent ones. As said above the hardest one to face is the 3..Bb4. The best for white is 3...c5. As 4.c3 4..dxc 5.nxc3 is beautiful. Put yourself in blacks shoes there. It wouldn’t be fun. I usually try for the scotch gambit but black can obviously force other stuff. After 3..nf3 I play 4.e5 going into a modern petrov. Now when this game started you think black said “I’ll play a petrov?”  ALSO don’t forget 3..d6 and now you’re in a philidor. 

Also the only reason I started playing it is to have multiple options from move 2 or 3 but to also be forcing in playing 2.d4. Instead of nf3 there is also obviously Qxd4, c3, BUT for fun don’t forget f4?! And a bunch of other moves if black doesn’t even take on move 2. I realized early that as a poor player like myself that the gray area is difficult  to navigate. So I’m trying to create as much gray area as possible for my opponents ON MY LEVEL as I’m more familiar in this gray area these moves create. 

There's no reason to change the move order. After 3...Bb4+ 4.c3 dxc3, White does not gain much after both possible recaptures. Sure, Black may go wrong, but at class level you cannot boast that "he got out of the book", since there is no such book at this level.

Bad? No, it is not bad. With optimal play white should not be worse, but the onus is on him. See the following game:

Pfren...what are your thoughts on 3...Bb4 than 4.bd2? I like c3 but at my level they always take that knight and I’m left with an isolated c pawn. What’s your take sir. 

You don't have to worry about an isolated c-pawn any time soon, since the c-file is not open.

4.Bd2 does not click to me.

If white exchanges, then somehow you will be able to get your pawn back, and claim you have achieved... well, nothing at all.

4...Bc5 is also annoying, since you will need to play a few clumsy moves to get at the d4 pawn.

Thank you very much Pfren.