So most of the more “deviant” sexual fetishes and fantasies, while shunned by society, are perfectly able to be done freely and legally in our private lives.
Violence on the other hand does not have that luxury, instead is restricted by numerous laws. You can have some kinky sex if you want with handcuffs and whips, but going to the local bar and punching someone in the face can net you some time in jail or doing community service. As such, where sex is more societal looked down upon, violence is more judiciously looked down upon. Since you can act out the sexual things that are viewed as deviant the need for other outlets is not as large or not as main stream. Since the outlets for violence are more legal it seems to vent itself into more main stream ways of expression through escapism in books, movies, video games, TV Shows, etc.
However, even in regards to violence, there is still taboos. Violence is usually either viewed gratuitously as a bad or frightening thing (such as SAW), in a heroic or brave thing (such as war games or cops movies like Die Hard), or as a retribution/just revenge thing (Boondock Saints, Max Payne). Other times the violence may be glamorized for the bad guy who is the main character but then tries to recant that life style (Samuel L. Jackson in Pulp Fiction) or we see the violence/evil of the main character be their downfall in some way (Scarface). Rarely do you see in mainstream where violence, channeled equally in a societal “negative” way, being glamorized. Instead it generally is images of violence that part of societies fabric wants to feel is “good” but knows legally is “bad” and thus this is their outlet for it.
The judiciously dissuaded compared to societal dissuaded is the big difference in them I believe. In one case you can do the act privately without life changing ramifications, in the other you can’t and thus an outlet needs to be made more readily available for it subconsciously through the society.