I have two problems with this.
First and foremost, Martin also had a right to defend himself and given the to circumstances of the two individuals involved, one being an unarmed minor heading to the home he was staying following a candy run to 7-11, the other being an armed self-proclaimed adult watchman who found Martin's trek homeward "suspicious" and worthy of "tailing"; I posit that Martin had the right to defend himself from someone following him for no apparent reason; whereas Zimmerman did not have the right to defend himself with deadly force against an unarmed person defending himself from Zimmerman. Which is the second issue I have with this -- that being that Zimmerman is the one to blame for their encounter. He was the one who wrongly assumed Martin was up to no good and possibly on drugs and he is the one who, against neighborhood watch procedures, pursued and confronted a "suspect." I don't believe the law justifies an indiviual to kill someone out of self-defense in a situation they themselves create.
No matter how this turns out, it's tragic for all involved. I have no doubt Zimmerman didn't seek to kill Martin when he first spotted him and in his prejudiced mind, believed he was performing a service for the neighborhood. And I do feel Trayvon was stupid for not simply getting himself out of that predicament when he had the chance. I know he never imagined it would turn out as horribly as it did, but he had already escaped Zimmerman's watch.
All he had to do was to go home.