Because censorship of violent games doesn't get rid of the problem.People with a predilection for violence can get their fix from any number of media outlets.You mention the choice games give you in an earlier post and I agree with your point..movies don't give you that choice (a comment I made in my earlier post incidentally

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However,games are only a small part of the problem.People in Western societies have witnessed violence in many forms of media for years..all sanitised and delivered to your comfy armchair via any number of news channels or newspapers.The explosion of the internet video culture and the ease of finding abbhorent video images for young people left for hours in front of computers by unwitting parents.I could go on..
People have become de-sensitised over the years and we only have ourselves to blame.Parents who buy/allow their children to play cert.18 games have a lot to answer for too.Many don't realise the dangers,believing games to be 'for kids'.They're the ones who need educating.
Saying that we can't police the distribution is a valid point..but then we suffered the same problem with videos when vhs became popular.Saying that censorship of this game is worthwhile if it saves one life is a difficult point to argue against (at least I think that was the jist of what you were getting at) but where do we stop? Ban violent films too such as Chucky etc? Because that might save a life.Oh and music that glorifies violence such as gangster rap? Because arguably that has more effect on impressionable younsters doesn't it?
So again..where do we stop? For the censorship of this game to be successful,it needed to be done with no-one knowing.Censoring it now only serves to make it an instant must-have item and guarantees it the infamy that no amount of advertising could have garnered.Censoring this game only serves to make it more attractive to the very demographic the censors are trying to protect.And in our globally connected,super-fast next day delivery culture,censoring this game will not stop it entering our homes.
I'll finish with a quote
'Censorship reflects society's lack of confidence in itself. It is a hallmark of an authoritarian regime.' ~Potter Stewart