Hackers ruin games for everyone but themselves, imo. I gave up playing a CoD game because of my issues with hackers in MW2, Almost every game I would have someone either aim botting, wall hacking, or just plain invincible.
Another game that is co-op, that I felt was ruined for me by hackers was Dungeon Defenders. Me and a friend bought it and played the first two worlds. I leave for lunch and come back. He now has gear that every piece gives him 10000 tower damage, health, and whatever other stats. All he would have to do is place one of his fastest towers next to each of the crystals and he could solo any level without the help of any of the other players.
He also called my bad since I refused to hack the game, and a threw away any non-legit item he gave me. This is also the same friend who called me a cheater for installing a respec mod in Torchlight 2... I don't even...