I think that when people view pornography it can cause apathy. I don't know if it's likely for pornography to also encourage rapists, but I definitely see it as a possibility. I have heard it argued that the regular viewing of pornography is a healthy activity, but I believe the opposite is true.
Pornography does not encourage rapists. Rape is not a sexual act. Rape is an act of control and domination. An act of evil people trying to prove to themselves and the victim that they have power and control over the victim. There is little in the act that has anything to do with sex.
Rapist have urges that stems far deep inside of them. Those urges have absolutely nothing to do with porn. Porn is a form of entertainment to people who enjoy it. Some people may have fantasies of having rough sex but that does not mean they are rapist. Rape is different.
Studies show that internet porn reduces the incidence of rape. So no pornography does not encourage rapists. There is a particular branch of feminism that tries to make it sound like it does, but the studies just are not on their side.
What causes rape? Lack of affective empathy combined with impulsiveness.