OK, it’s late, and probably no one will see this post, but I have read some non-FR message boards and I see a pattern.
In my upper-middle class white world, the person responsible for starting a fight is the first person who physically touches the other. Words, threats, “sticks and stones” don’t count. Nothing matters until physical assault occurs. In that (my) world, Martin probably started the fight.
In the world of many of the commenters anti-Zimmerman, Zimmerman became the aggressor by simply following or verbally confronting Martin. They believe that this was the initial act of aggression, and that Martin was then allowed to physically “defend himself” from this “stalker”.
The differences seem to be based on different rules of conflict in societies and culture. Being yelled at, stalked, or harassed is not a license for physical aggression in my world, but it appears to be in Martins and his defenders.