If you aren't on your own property, and the guy is unarmed, it would have to be a very extreme case for me to ever be able to justify deadly force.
I've seen the bloody pictures of the front and back of Zimmerman's head, and I've read the interviews of some of the eyewitnesses describing Martin pinning Zimmerman down and punching the crap out of him. Of thats what happened, then it seems pretty extreme to me.
Now, if you're Zimmerman, are you thinking at that point: "golly, I wonder if this is extreme enough for me to shoot this guy?" Probably not. You'd probably shoot him. Or at least you pull your piece and tell him to back the eff off, and pray he doesn't grab it from you. Personally, I'd rather pull the trigger than take that chance.
And please, save the oh so predictable response "we'll I wouldn't have stalked the kid and started a fight with him." Ive not yet seen a shred of evidence that Zimmerman started the physical altercation, and there's nothing wrong with asking a stranger what they're doing in your neighborhood. If there was, this would be a much easier case for the state.
As for the "skittles and ice tea aren't a weapon" tripe, jfc. Martins fists evidently were weapons, unless you're also suggesting Zimmermam did that to himself.