You’re talking to a child
Now a harder suggestion: Police yourselves. When an impetuous member of Anonymous “revealed” the wrong person as Michael Brown’s shooter, many other members aggressively and publicly condemned the member. You’ve got to do that, too. When the more infantile and hateful members of the online gaming contingent harass a woman, you should remind them what the actual goal is, and tell them that they’re tripping themselves up. Remember that you’re talking to a child, in spirit if not in actual fact. If you police yourselves, Reddit and Steam moderators won’t have to. This is not an easy task, but it is possible. Self-organizing communities are one of the miracles of human civilization.