This is a classic example of the, support-homosexuality-or-else mindset of most of the glbt community. If the situation was reversed, and someone attacked an anti-Christ, pro-gay banner, they would be tackled to the ground by police. I'll bet that the homofascist attacker is never prosecuted for his actions either, like an "anti-gay" person would be if the situation was reversed.
If, twenty-five years ago, someone had taken me to into the future and shown me this event, I would've thought, Why is this group stating the obvious about marriage? And, Is this guy (the attacker) some sort of deranged polygamist or something?
More info here.