What's wrong with the King's Gambit?

What's wrong with it? The pawn on f4 is hanging...

lol, yeah the problems with it are:

1) Loses a pawn
2) Moves F pawn, weakening king

Now sure there are some good things about it too, but you really just can't get away with it at the top level. (Other than as a surprise weapon if you're feeling ballsy.)

If you're white and SF is evaluating your position as -0.6 after 3 ply, you're probably not playing the soundest opening.

That said, I'm sure you could get away with it at the U2200 level if you know the theory and plans well. If you really like those type of sharp openings, go for it.

In many other openings you would pay some bucks in order to bring your opponent to weaken his position by moving the f-pawn...

Even in TCEC engine competition white wins with it despite the initial -0.6.
Here another example at top level and against a good defender.

Nigel Short once said that the main advantage of the King's Gambit is that there are so many refutations that Black will lose on time trying to pick one. Every joke has a grain of truth, and all that.

After 2...ef4 3 Nf3, Black has at least six moves that, at the minimum, equalize,

@mn8 And that's why you play 3. Bc4 instead of 3. Nf3

Sure, but Black isn't exactly lacking tempting options there either.

Black can gain equality with 3. d5 or 3. Nf6, the other moves (Ne7, Qh4+) look pretty good for white to me. Black gets equality, but white will get an extremely tactical and wild game, which is almost certainly what he's looking for with the move 2. f4

@Water_Flame or black just plays the line i gave in #5 and is better.

I'd say that's equal, maybeee slightly better for black. However white doesn't have to immediately push d4. Playing 4. Nf3 g5 5. d4 looks better imo and white should be at least equal