...gh5 winning the exchange. White has not developed his kingside pieces. So the time it will take to get them active gives you more than enough time to prepare for any kind of attacks against your weakened pawn structure.
White has 2 pieces "attacking" your kingside. You have 5 pieces defending your kingside. Simple math. You take the rook winning the exchange. Now white has 1 piece on your kingside while you still have 5. Math...its a wonderful thing :-)
There are fundamentals like not moving the pawns in front of your king. But you'll learn when you can bend these rules and have better judgement over when it's worth it. Winning a piece with damaged pawn structure is usually worth it unless your opponent is currently assaulting your king with his pieces.
In this case, his knight/bishop/rook are still on their starting squares, so you are completely safe. Also, queens are traded so any future attacks aren't as deadly.
I went to the analysis board.
After ...gxh5
Bxf6
I'm trying to figure out how to organize a defense.
White's f pawn will eventually dislodge ...Ng6
Maybe get the knight to g7 which will take a lot of time.
I was black, up two pawns, better developed, queens off the board. I had a choice between trading bishops or winning the exchange. But taking the rook meant wrecking king safety. I choose to trade bishops and maintain king safety, especially the dark squares around my king.
But surely there are times when foregoing king safety leads to a winning position. Say, queens are on the board, no rooks, and you can capture a queen for a bishop. I know it'll depend on pieces left, pawn cover, etc..., but when do you sacrifice safety for material advantage?