As many have said...it is not sacrifice but exchange..it is not illegal....it has nothing to do with manners...
Is sacrificing Q for Q bad manners ?
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No fair trying to win.
I think the killing happening in wars are quite bad. Why can't those who are white and black just have peace and agree to a draw without any blood spilt? Letting your queen get killed just to kill the enemy's queen sounds horrible. Are the rest of the army really going to follow a leader with orders like that?
Let's change the rules of chess to not let players capture pieces and remove the checkmate rule. That should solve this problem. 
Martin0 wrote:
I think the killing happening in wars are quite bad. Why can't those who are white and black just have peace and agree to a draw without any blood spilt? Letting your queen get killed just to kill the enemy's queen sounds horrible. Are the rest of the army really going to follow a leader with orders like that?
Let's change the rules of chess to not let players capture pieces and remove the checkmate rule. That should solve this problem.
I prefer blood on my battlefield. lol, jk jk. I agree with you !!!
As an aside, if I'm only slightly ahead in material, for instance, by a pawn or two or the exchange, I usually find it a bad idea to deliberately trade off pieces. Instead, if possible one should continue to work out well-motivated attacking plans. In order to avoid them, the opponent will often have to trade pieces in a manner that further damages his position. There are exceptions to this but usually, the equivalent of 4 against 3 is stronger than 3 against 2, due to the extra possibilities afforded by the greater amount of material on the board.
I agree with not deliberately trading when you're up a pawn or the exchange, but when you're up by 2 pawns I'd say it's a good time to start trading pieces. Winning an endgame with 2 extra pawns is pretty easy (at least in my experience), a lot easier than winning with 1 extra pawn or a rook for a minor piece. And, if you manage to trade off all other pieces, K+2P vs K is always a win, while K+P vs K could be a draw depending on the position, and K+R vs K+B/K is pretty easy for the weaker side to defend and force a draw.