The act of murder is less likely than the act of sex. Kids watch people killing other people in a video game they usually wont consider doing the same. Kids watch people fucking and it just adds to their desire to wanting to have sex.
On the basis of what man? Like kids won't consider doing the same re: violence? There's a lot of effort in society and the media to blame JUST these occurrences on violent movies/videogames. I don't particularly buy that as it's pretty much a moral panic, but it's a bit weird to claim that it doesn't desensitise children to violence in the same way that seeing sex does with procreative activities.
Plus tons of the GCSE kids I see talk about "Killin' a Taleban" and shit, mostly influenced by like Call of Duty. Fuck, my youngest bro was considering being a soldier for a while on the basis of playing that game.
PS: Kids are always going to want to have sex (or, rather, to be seen as being in the know sexually), regardless of seeing it in videogames or not. They're bombarded by it via television, advertisements, and movies. It's also been the subject of schoolground boasts even when I was young and videogames consisted of moving left to right jumping over shit.