I'm not seeing the lack of the same self-defense. Unless security watches and even public curiosity about unusual behavior is declared illegal or aggravating per se, there is nothing wrongful about being armed with a gun, profiling, stalking, and confronting someone where there is reasonable cause for these behaviors. As for the shooting itself, it doesn't even matter if those behaviors were wrongful, if they can't be used as a legal justification for St. Trayvon to physically attack Zimmerman. Once that attack takes place, Zimmerman is under no obligation to allow himself to be harmed or killed - none whatsoever. Thus self-defense trumps again.
An agressor loses the right of self defense.