Get real. A black kid is walking down the sidewalk in a predominently white neighborhood. He notices a car, with a man driving, following him. Ya think he might get a little concerned, frightened and take a detour to lose the tail?
Using your logic, why didn't Zimmerman pull up alongside the kid and ask him what he was doing?
If you're frightened by/afraid of someone, you don't then stalk and jump them, pummelling them mercilessly.
What planet do you live on?