I guess I see it like this...
if I am driving past your yard, and I see your dog sitting on the porch.
I stop my truck, get out and run at him as fast as I can. He retreats two blocks and hides under a porch.
I chase after him and spend 2 minutes checking every porch until I find him. AH-HA! And he springs out and bites me in the nose. So I shoot him in the heart.
I mean, yes, it was legal... but I did everything I could to create and provoke a situation of fear and confusion, and I intro'd a deadly weapon into it.
Without zimm doing things like staring kid down, jumping out of trucks, chasing and confronting him - in the confusion of rain and night - nothing happens that night.
Trayvon just turned 17 and was walking home in the rain with a snack. Out of the blue, a great unknown threatning force chased and cornered him. It's not murder, but pure self defense in the same league as zimm walking to church and trayvon jumps out of a car and starts swinging? no. It's a gray area. he created the situation and provoked an attack, and entered it with a gun.