A comment I feel should be reposted here for the benefit of our less able rhetoricians:
http://www.sankakucomplex.com/2010/02/18/save-the-children-ban-loli-manga/#comment-438047
The "catharsis" argument that loli manga serves as an outlet for lolicon who might otherwise be drawn to real children is deeply flawed and you should not propagate it.
If you are making this argument, you have just conceded that lolicon fans are actual potential child rapists and the only thing stopping them from attacking children and fulfilling their disgusting lusts is a supply of vile pornography. All this suggests is that they should be locked up to prevent them committing crimes when they run out of manga. It singles them out as immoral perverts held in check only by fictional proxies.
Similar arguments for violent games are never used. Playing violent games or watching violent media do not, it is said, predispose people to violence, nor do do they prevent violence by those who might otherwise do so. Defenders go to great lengths to point out there is no link at all between the two.
"GTA helps prevent murder by keeping killers off the streets and letting them sim-kill at home" - I think not.
You should stick to similar arguments to those used in similar debates, based on freedom of expression and there being no demonstrable causal link between media exposure and behaviour. Otherwise you are simply propagating a harmful fallacy which only harms the people you are clumsily attempting to defend.
Please note that I am only addressing the subject in terms of rhetorical tactics - the scientific question of whether fictional media predisposes people to action (it may well do, else how can we explain religion?) is not relevant to opponents, so it should not be relevant to defenders intent on winning a debate and putting the enemy to flight.

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