Reason why a kingside attack is not justified Given my lead in development in this game, the presence of an advanced pawn on the 5th rank and the arrangement of the pieces toward Black king, I think that an immediate kingside attack is justified.



In the game I ended up playing a move which I do not like very much now that I think about it (6.Bg5).

However, thinking about it now, I believe it would be best if I had started playing g3 with the idea of defending the knight in my next move (Nh4) as well as to support an upcoming advance f2-f4.

However, Stockfish seems to prefer to slowly manoeuvre on the other side of the board with b3, Nc3... but all of these moves seem to ignore White's lead in development. I can see that moving my pawn to b3 will eventually allow my light-squared bishop to be placed on d3. But I believe that is too slow.

Why is a kingside attack not justified here?
There is no king on the kingside yet to attack. Black might very well castle long in which case your attack is aimed at nothing and might potentially weaken your own king's safety.

5....c4 is premature and unnecessary. It loses the pressure on the d4 pawn and loses a tempo for development. 

A very typical reply to such pawn structure is b3, which is based on the fact that black cannot stabilize the pawn on c4 as after 7. b3 b5 8. a4, a6 is not an option because of the potentially hanging rook on the a file (after axb5 axb5). 

The situation would be different if black had for instance already played Bb7 which would defend the rook.

So all in all, b3 is a natural plan, which will in the short term weaken black's pawn structure and give white an advantage.

The other option, kingside attack, with f5 eventually is not bad per se, but you should probably wait until black has castled short. Also it takes a lot of moves to get any kind of attack going.