Feminism

Transmen do face discrimination, and it's often times violent, though you're correct, they generally aren't the focus. I think that there are a couple of factors at play with the focus on transwomen. The first factor is, from their point of view, transwomen are viewed as an attack on masculinity, both as a rejection of "traditional" masculinity and the "scary" thought that they might be attracted to a transwoman. Furthermore, there is an often unspoken acknowledgment among transphobes of different stripes that men are inherently dangerous, that their violence is barely contained by the rigid structures of society. In this world view, a transwoman is both rejecting her masculinity while also attempting to subvert the structures of society to act out on her violent masculine impulses. It's contradictory, moronic, and plain wrong in the assumptions made, but that is their world view.