Your username would imply you are male. Thus, you literally oppose Men's Rights groups... as a man? That's not unprecedented, as there are women who reject feminism in its many flavors, but by doing so, you're saying that there are no issues at all that men need be concerned about?
I can not talk for GP, only for myself. But you are oversimplifying the situation.
I'm a man. I'm against the mens rights groups that I know of. Not because I believe there are no problems. But because I believe that those mens rights groups I know about do their cause a disservice. Instead of pointing out rationally the existing problems, they pretty much always exaggerate, go off on tangents and generally come about as weirdos and nutters.
This, by the way, is also true for at least some of the more extreme feminists.
But there are not only extreme feminists, but also moderate one. Yet with mens rights activists there doesn't seem to be a middle ground.