So if two teens are wrestling around and one gets a scratch or two, it's ok for the one with the scratches to pull a gun and shoot the other? No reasoning at all?
What would this lead to? Would we be saying anyone that claims they are super sensitive, such as GZ, should be allowed to kill anyone that hurts them in any way whatsoever, because the hypochondriac goes into a tizzy fit over any minor hurt? What about minor insults? Where do we draw the line on reasonable expectation that you are gonna die if you don't kill the other person?
No reasoning at all? Almost everything I have written is based on case law, which is extremely well reasoned. In fact, it is so well reasoned, it has endured for centuries in English common law. It would lead to what we already have.
I believe that it is reasonable to fear for your life when another is arguably beating your head into the concrete. You don't. What is reasonable to one may or may not be reasonable to another. But I think you are being disingenuous as to the extent of what Zimmerman's injuries could have become. Did he have to wait until brain matter was hanging from his ear to defend himself? Cranial injuries aren't "minor hurts;" they can kill you dead as a hammer.