Something is special about sex. People have sex. People don't kill others (generally). Compare how many people you personally know that have had sex vs how many people you personally know that have killed someone.

As the study above points out, violent videos games don't make you more violent but I'm pretty confident sexy media (games, movies, music, etc) make people more horny and therefore more likely to seek out sex. Also, since sex is something people do in the normal course of their lives (vs violence which is not a normal part of someone's live) the media they consume is more likely to influence their behavior. It's a manual for something they hope to participate in vs violence, something they don't hope to participate in.