The killing of Trayvon Martin is a tragedy. Also the average person does not know all of the facts of what happened in that encounter. But based on what is known one conclusion can be immediately drawn: the "Stand Your Ground" law that exists in Florida is not to blame.
People are blaming that law, and it appears that George Zimmerman may plan on using it as a defense if charges are brought against him.
A "Stand Your Ground" law only applies if the person doing the shooting does not initiate the encounter. That law only applies if the action is defensive. If someone initiates an encounter, and the confrontation escalates over the course of the encounter, there is still no interpretation that leaves defensive lethal force on the part of the person who initiated the encounter.
George Zimmerman, if the press reports are accurate, was trying to act as a neighborhood watch. At some point he confronted someone he thought was suspicious in his neighborhood. He initiated the encounter.
Those who are claiming this is the result of "Stand Your Ground" laws are deliberately obfuscating the issue. Their purpose can only be to argue against this particular aspect of self defense, so as to confine all defensive actions to those by the government on behalf of the people it allegedly protects. It is unfortunate that George Zimmerman is falling for that obfuscation as his doing so only adds fuel to those making the claim.
Vigilantism isn't the same as self defense, and "Stand Your Ground" and other related doctrines don’t apply to the vigilante. There are times when vigilantism is valid, but it should be clearly identified as such and not confused with a purely defensive action.