I agree with the above.
Shooters, yes even the gruesome ones, thought me a lot of things. Besides the fact that they enhanced my ability to react and the speed with which I react it also thought me to look ahead.
In other words, games thought me that actions have concequenses. Sometimes these can be good and sometimes these actions would basically kill me in the game.
Of course I could go on and on, but the principal is this: Gaming can bring you a lot of fun and friends aswell as teach you things as long as you keep the very thin line between reality and fiction intact. Your parents worry about this, which in fact is very natural and understandable, but if you keep it at bay and turn the gore off I'm sure everything will turn out just fine