Sicilian dragon, When white castles kingside

Now, I know the main Idea of the dragon is to use the dragon bishop and open C file  to launch a queenside attack, ofter via a pawn storm, but what do I do if white castles kingside. I have heard this is inferior, but why?

Well, the reason it is regarded as inferior is because black can achieve "equality" more easily in those lines. It would really come down to a matter of style if you wanted to play these lines. I believe that the lines where white is commonly found castling kingside are the classical, the levenfish, and the Tal variation.

Well think of the kingside castle this way: at least your opponent didn't play some anti Sicilian....

By castling kingside, white just makes the game less sharp at the cost of diminishing some winning chances.

first you have to know why queenside is better to understand why kingside is lesser.. the reason is simple- in the dragon white has a space advantage (temporary) and black has a central pawn majority (can be longer term)

so if white sits around and only casually develops his pieces, black will eventually catch up in developement, then space, then will use his two pawn center to load up on the key squares.

of course theres some still some decent plans kingside, but in general its slowly giving black more life. as white you should develope the minor pieces,castle queenside, throw some pawns at the king, trade of bishops, and sac .. sac.. mate :)