The only thing you'd lose when playing Manhunt 2 is however many minutes you bother to play it for before falling asleep. You can never get that time back you know?
"A normal sociable person who plays such a game for a few hours a week won't be affected. A person who has no friends, stops in and plays games all the time might be affected."
Your argument lacks any kind of reasoning. I used to (I stress 'used' to) be a hardcore gamer and as you delicately put, stopped in and had no friends (offline anyway) but was never tempted by games I played to replicate my actions in real life. The simple fact is that I am not mentally unhinged, so I have no difficulty separating games (or for that matter tv/film) from reality.
The type you refer to are the same type of people who send death threats to actors playing certain characters in soaps, because they hold them responsible for the actions of their character. The people who cannot separate one world from another because their brain is incapable of doing so.
It's basically the standard argument that people use to blame tv/film/games for all of societies violent problems, but the simple and unavoidable fact is that the problems we have in society are a lot more serious and complicated.
Not that I disagree about Manhunt 2, but for different reasons. I'd simply like it to disappear on the basis that it will be rubbish, which in fact it probably will very soon after release.