and all Zimmerman had to do was stay in his car and nothing would have happened either.
Maybe you and I think he was being a bit of a wannabee cop, but he had still volunteered as a neighborhood watch, facts that are not in dispute.
Last time I checked, walking without actually threatening someone is not justification for use of force, certainly not to the point of confronting and violently pounding the walker's head against a sidewalk.
Zimmerman may not be exactly a model citizen, but the fact remains that the real aggressor, while regrettably dead, is dead directly because of his own actions, not because of the actions of Zimmerman.
The key thing here is that the initiator of deadly force, as slamming a man's head against a sidewalk certainly is, wasn't Zimmerman.
As was already pointed out above, all Martin had to do was continue walking all the way home and not a thing would have happened in the end.
ZERO
If being followed or merely believing you were being followed were the only legal justification for use of deadly force, just any person could kill someone else, then claim that he was in fear for his life and go free from prosecution.