I actually completely agree with equal rights, equal fights, BUT I think it means more than just boys fighting girls. It should apply to everyone. For example, if a 100 lb girl was to fight a 175 lb male, this would no way be an equal fight, and at the end of the day, everyone will call the guy a women-beater and will definitely take the girl's side. But say we apply this same situation to a 120 lb guy fighting that same 175 guy, I believe this situation is no different than the one I just described. Yes, they are both male, but in no way at all is this an equal fight. But when the little guy gets beat down, most guys and even girls will say he deserved it for starting that fighting, and will take the bigger guys side. This is not equal rights.
That being said, I believe if someone starts a fight with you regardless of gender, you should try to keep out of it. But if they continue, then anything that happens from that point on this their fault.