2. Bc4 !? against the sicilian

Don't know if it i too late but I would like to disagree with the titled players so far. I was wondering myself the same issue, namely
1.c4 e5 2.Nc3 Nc6 3.g3 Bc5 is the Karpov defense in the English Opening. Therefore, if even with 1 tempo down it is a good option, it cannot be bad. I remember carlsen even trying to win that way against anaother 2700+ player as black. So in short I claim that 2.Bc4 in the sicilian is an acceptable move.

Also, I do agree that compared to the other variations (like 3.d4, 3.Bb5) it should be less 'painful' objectivly for black. Meaning that 1 tempo in the Karpov variation of the english opening for black is less valueable than e.g. in the Dragon variation where black plays e5, d5, Nxd5. So with good preparations, or very good play Bc4 is easier to counter than the mainlines in terms of reaching equality.

Having said that, do you remember Carlsen abandoning the mainlines just to play? To get rid of theory and win by skill? Or the fact that even though 2700 GMs still play open Sicilian occasionaly (since e.g. Gelfand and MVL are using it), all the Top 20 players uniformly are only playing Bb5 stuff against the Sicilian? That i because the mainlines, Najdorf, Dragon and Sveshnikov particularly are theoretically analysed to a dead draw if you just remember all the lines, which the 2800 Elo players indeed know and do remember. By your argument them playing Rossolimo (3.Bb5) instead the mainline would be wrong, or less good. And still they do. For the same reasons, though to less extent I cannot agree with you about '2. Bc4 is a wrong move just because engine says it is not the best move'. This is about the elite chess

Now back to the reality. The OP is an 'amateur' in terms of perfect play. Up to titled players level like you and me you do well just by following a strategy. Sure you might chose not the most critical strategy (aka mainline), but still it is a strategy. And if you perform well in it, if you become an expert with your weapons, you are as dangerous as a guy who learned but not really understood the mainlines. Not to mention black usually does not encounter the Karpov-line as white. Nor does a sicilian player always play 1.c4 himself to know the position to begin with.

And to add in the end, if you would argue that he is a beginner, he will fail and do mistakes, then you are right. But a)so is his oponent and b)will it matter if he fails 2.Bc4 or the mainline? And finally, even if we talk about titled players, between us, I play french. We do agree that 3.exd5 is a 'bad' move for white if you play for a win. And still, there are titled players who do specialize on exactly this kind of positions (e.g. Latvian GM Miezis, 2500), they absolutely do understand that the position is equal after the openings, but their skill, experience and middlegame understanding in these familiar positions allow them to win regularly. Because equality is not the same as a draw. With this I would conclude it and agree with OP, Bc4 is a plausible move vs the Sicilian, if you play like in the Kaprov system for black. (e.g. Nf3,Nc3,0-0,Re1,d3, Nc3-e2, c3,d3-d4. And a3+Ba2 if black plays a6+b5)

The Bowder attack is like the London System.
Compare
1 e4 2 Bc4 3 Nc3 4 d3
with
1 d4 2 Bf4 3 Nf3 4 e3.
The London System was also disrespected until Kramnik & Carlsen pleyed it.
The Bowder attack can transpose to a Nimzovich Indian Reversed if black played ...d5 and white goes Bb5
Compare
1 e4 c5 2 Bc4 e6 3 Nc3 Nc6 4 d3 Nf6 5 Nf3 d5 6 Bb5.
with
1 d4 Nf6 2 c4 e6 3 Nc3 Bb4 4 Nf3 d6 5 e3
White has lost a tempo with Bc4-b5 in the Bowder, while black loses a tempo with ...e6-e5 in the Nimzovich Indian Defence, as in the way Nimzovich himself used to play it.

@Strategymaster Your example of the Karpov defense is different - like I said, I think the only times when white/black might want to put their bishop on c4/c5 would be when black/white has already committed to g6/g3. In your variation white used his extra tempo to commit to 3. g3, making 3... Bc5 more logical and perhaps even stronger than if white had not made any third move at all...

And I suppose definitions of "good" vs. "bad" moves vary. If you play an "objectively" worse move, but you surprise your opponent with it, and you are better prepared in the resulting lines and positions than him or her, then you might achieve a higher win rate against the same opponent with this variation. But like I said, I'd similarly rate Carlsen's chances against any 2700 player pretty high even if he plays 1. g4, for the mere reason he is Carlsen. I'd still call 1. g4 a bad move though.

In any case, like I said, I'm not saying 2. Bc4 is losing in any way, and with good preparation and as a surprise weapon you may score very well with it even against strong players. But for me, talking about "good" vs. "bad" comes down to the highest levels of chess, with strong players who play the best moves most of the time. In that scenario I believe 2. Bc4 is not a challenging move, and that's why you won't see it played by 2800+ players.

@tpr That is again different - after 1. d4 d5 in the London system, black cannot block the f4-b8 diagonal easily anymore, so the bishop on f4 puts clear pressure on c7 from the start. The equivalent version of 1. d4 d5 2. Bf4 with 1. e4 would be1. e4 e5 2. Bc4 which I think is much more sensible than 1. e4 c5 2. Bc4. (1. e4 c5 2. Bc4 is in a sense comparable to 1. d4 f5 2. Bf4 against the Dutch, which I don't think is very logical either. Then it's also not called the London anymore, but some weird sideline of the Dutch.)

It's rather like playing Bf4 in the London when Black hasn't commited himself to d5 and kicks the Bishop with d6+e5 in the corner.

It's a legal move, sure.

lichess.org/forum/game-analysis/neutralizing-the-london-bishop#1

1 d4 Nf6 2 Bf4 is often played and black does not always play 2...d6 then.

2 Bc4 is a developing move, prepares castling, fights for square d5, this cannot be wrong.

It is even playable in reverse, i.e. as black with one tempo less

It is playable. 2.Be2 is playable, 2.a3 is playable, everything is playable. I wouldn’t play it though because I consider the alternatives better.

Yes indeed, objectively 2 Be2, 2 a3, 2 Bc4 and 2 Nf3 are all equivalent, transforming a position draws with best play from both sides to another one drawn with best play from both sides.
2 Nf3 is more fashionable, but fashionable is not the same as better.
Subjectively 2 Nf3 may be better in the sense that it statistically offers more chances to win i.e. more opportunities for black to err.

#17: 'It is playable. 2.Be2 is playable, 2.a3 is playable, everything is playable. I wouldn’t play it though because I consider the alternatives better.'

Just wanted to make you aware, aswell as everybody else, that this is not an objective statement, nor is it a truth, but a pure opinion. Which would be a useless statement, since we are not pulling a poll but looking for arguments, which you thought your statement would be itself.

To make it clear, with the same logic I can say 1.e4 is a good move, I would not play it though since I consider 1.d4 better. Or to use your method is, 1.e4 is playable, 1.g4, 1.h4 (to throw a good move with shitty ones into the same basket as you did), so since 1.e4 is dismissed by me putting it into the same category with these the reader of my lines would agree with me that 1.d4 is better than (1.e4,g4,h4). Won't work here since everyone should be smart enough to know that 1.e4 is a good move, but for someone who does not (like guys who don't know about 2.Bc4 in sicilian) might agree for the wrong reasons.
What do we learn from that? Nothing, the statement sadly is worthless for the sake of argument.

50 years ago you considered people NOT playing 3.d4 against sicilian cowards. Either 2.c3 or Nf3 were the only right options. Now Bb5 is on the rise. Or for the very same reason the Taimanov is trendy since it does NOT allow the seemengly bad Bb5. You can consider Bc4 bad now, but I bet if Carlsen played it, it would be mainline?!?! Just remember Carlsens 1.e4 c5 2.Nc3 d6 3.d4 cxd4 4.Qxd4 Nc6 5.Qd2 with b3 to follow. Or Carlsens 6.a3 in Najdorf which was considered a beginners mistake (against equals). Chances are pretty slim that Bc4 gets to that point, but nevertheless you should not disregard it (put it into same bracket as really bad moves).

And a final point, I remember myself having 2200 Elo and seeing no advantage for white in 1.e4 in many mainlines. You could actually say I saw no advantage playing 1.e4. Moreover I could even prove my point to quite a lot of players below my strenght. That does not mean I was right, correct? I was just too weak to see further, since there were players beating me still with 1.e4. So I will claim it is at least possible you don't see the strenghts of 2.Bc4. And of course you are right that is your decision to play the 'mainlines' instead, but that does not mean this is an argument for you to discourage other players to play it (as you do with your statement). I mean for the sake of argument I can say "mainline, Bb5 and Sveshnikov are analysed up to a draw, while 2.Bc4 is not. What would be the reasonable way to play for a win: show your skills and beat him or jsut to hope he does not remember the crucial lines?"
My whole point was to claim that Bc4 is wrongly regarded as inferior, and your statement #17 just bypasses all my effort so far as if you did not understand them at all

@thijscom
Would you have said the same about 6.a3 in Najdorf or 1.e4 c5 2.Nc3 d6 3.d4 cxd4 4.Qxd4 Nc6 5.Qd2 with b3,Bb2 and possibly 0-0-0? If you would have asked me I would consider them exactly like you described 2.Bc4. And nevertheless, they were played by Carlsen and repeated by 2800 players (Fide Candidates 2014?). Even more funny it is, that it was not by any 2600+ players, but exactly by the very best, for exactly the same reason- mainlines are dull. 2700 players still fight the mainlines and hope to outprepare/outsmart the players which is possible by imperfect play. While the best of the best seek a whole other way, like the one I mentioned above.

How would you see 6.a3 in Najdorf now, after 2800 players played it, against themselves (not weaker oponents). Is it now 'playable'? 'Mainline'? You can hardly change righfullness of a variation in 2 days just by the fact that some players did play it. It was either good the whole time, or it is still not. In the first case your/our evaluation is plain wrong to begin with, which could be the same with 2.Bc4. In the second case you would say just because 2800+ players play it does not change a thing. Which would make your whole point ('Why do 2800 not play it'?) invalid.

Or to put and end to it, Bc4 you cannot deny with arguments, but only moves. Lines, variations. And exactly here I claim that it might be 'easier' to equalize than the mainline (e.g. only till move 15), but on the other hand you start from scratch (from move 5 instead of move 20-25 like in the mainlines), meaning it is still the same amount of work. Which, if that is true, which I am convinced of (but can agree to disagree), 2.Bc4 is as tough a try to win as the others. And not just a random beginner move