Violence I think holds many more issues in it than sex does.
My primary problem with this poll, and the culture of the US in general, is that BECAUSE we are so closed off about sex, because kids dont grow up understanding sex can be a good thing, a bad thing, etc. we have teens having sex, and having kids. I dont know about any of you, but I remember my sex ed class in middle school (and high school even) to be little more than essentially scare tactics (OMG LOOK WHAT DISEASES YOULL GET IF YOU HAVE SEX). Just like the DARE program (anti-drug use program for those not in the US). I do remember my first time having sex and my first time smoking pot, and thinking that the "educations" I got were a joke.
Yes, there are sex video games, obviously not for sale at your local Best Buy or Wal-mart. AFAIK, many are just as excessive sexual fantasies as FPS's are violence fantasies. I could argue that "sex" games could fill the same niche as violent FPS's. An exotic fantasy that you wont get to live in real life.
Violence is "always" a bad thing, but we grow up understanding it to be a common thing. Reporters dont even flinch when they report on another school shooting, hell, you just lost a kid in a school shooting? Katie Couric will come to your front lawn, looking for an interview. Violence is accepted.
Simply put: I think my country has an unhealthy attitude towards sex. Even more so towards "deviant" sex. And a very unhealthy attitude towards violence.