I don't disagree with much of your analysis, but do think that the link between viewing violence and aggressive behavior is complicated, and that the evidence for at least some causal relationship is there. When looked at in randomized controlled studies there is a causal link between media violence and aggressive behaviors. These are all lab setting, of course, and as this article below states, the real world influences are more complicated and less clear cut.

http://www.surgeongeneral.gov/library/youthviolence/chapter4/appendix4bsec2.html

I'd also agree that viewing a murder doesn't mean that someone will go out and murder (as you point out most people aren't murders). But what if viewing murders every day on TV make a child or an adult more likely to hit another person, or perform more lower level aggressive acts? Again, I think the above article is good for pointing out that we can only draw cautious conclusions between TV aggression and behavioral violence and that frequently the message that's taken from those studies is that media violences causes aggression, full stop, end of discussion. That's much too simplistic. But the link is worrisome enough to me that I don't want my 5 year old watching media aggression.

Perhaps another thing to think about is that aggression, by definition, is hurtful to other people. While sex can be hurtful, and can be a bad thing in the wrong context, and isn't something to encourage young people to do, etc.... in the right contexts it's not hurtful and is part of a fulfilling relationship. I know plenty of the sexual images portrayed in the media aren't so healthy, so that's something to pay attention to when thinking about what kids are exposed to. But I'd certainly rather my child saw nudity and even healthy sexual relationships than excessive violence.

I appreciate your post--it made me think!