"Humanity tends to be communal and, well, for lack of a more flattering adjective, mobbish, believing that another person is similar to oneself... When those beliefs are challenged, in this case, the belief that "everyone is a sexual being", the majority recoils and looks upon that "abnormality" as the betrayer and counterattacks the Other."

In my opinion, it boils down to inherent xenophobia. It may have served our monkey ancestors well to get them to compete for limited resources against other monkey ancestors, but it makes for a serious issue now.