Because sexual intercourse is more easy to do than killing somebody. We have an overpopulation problem. We don't want kids fucking.
I don't think it is has much to do with puritans. That's just something people in Europe say because they're heard it from someone else who heard it from someone else. A lack of critical thinking will do that.
Sex scenes also do little to move the plot along, whereas violence is usually a part of the plot that contributes to the overall tone of the film.
For example, in a film like Wall Street, sexual intercourse and nudity do absolutely nothing to move the plot, yet I can recall two examples where they occur prominently. 1) Bud Fox's unnamed sexual partner rises from the bed, naked, and walks off camera. Bud gets up from the bed and checks his computer to see that it is Gordon Gecko's birthday. 2) Bud Fox gets into a limousine at the behest of a prostitute hired by Gecko to show Fox a good time. It is implied that she performs oral sex on him, though it is no explicitly shown.
Neither of these scenes contribute to the plot of the film.
People raving about "puritans" need to stop for a moment and think.
On another note, I tire of people who claim that sexual scenes are edited out/censored but violent scenes are let through. This is untrue. If you have seen the movie Gladiator as many times as I have, you would know that extensively violent scenes are often shortened or removed entirely from the film's run on TBS and TNT.
Now some of you on here blaming puritanism for making people feel ashamed of their bodies. That's not fair. Some of you NEED to be ashamed of your bodies.
But in conclusion, sexual scenes rarely move the plot along. There are some films that I've heard of, like Irreversible, where sexual scenes are pretty much the point of the film. A woman is raped and people take vengeance on one another for it. It makes sense. The graphic nature of the scene serves to show the viewer how horrific rape is.
But Angelina Jolie's tits in Taking Lives, while nice, do NOTHING. They distract both the male and female viewers from the plot of the film. The plot of the film itself sucks and we can tell right away that Jolie's breasts were shown to salvage an otherwise mediocre attempt at film making. Furthermore, I feel nudity in modern films is really just a lazy way to draw attention to the film.