RTB...
That right is not being challenged. The question is whether or not it is reasonable to repeatedly follow someone who has committed no crime, to the point that they are so afraid that they actually run away, then continue to pursue them -- against police advice -- and when you catch them and a scuffle takes place, kill them as your first and only effort at "self defense."
Now all this might be reasonable, PERHAPS, if the defendants story remained consistent and plausible. It is simply a fact that Zimmerman's story evolved over time and it does not match the physical evidence at the crime scene. This happens with every case, and it's expected, but some of the inconsistencies are significant and suggest that Zimmerman is not telling the truth about some very important details.
The EVIDENCE for Zimmerman's defense is his word. That's pretty much it. We don't know who was yelling, we don't know who was on top, we don't know who threw the first punch or even if any punches were thrown at all. We do know that Zimmerman's claims that he had been punched twenty or more times in the face are likely false -- there is no evidence for this and plenty of evidence it never happened. Equally questionable is the claim that Martin was repeatedly pounding his head on some concrete. Maybe it happened, but the physical evidence doesn't support it, and it certainly was NOT happening when Zimmerman pulled the trigger.
Again, this case is not about the right to defend yourself. This case is about an unarmed dead teen. IMO