Self-defense is still an affirmative defense and it's not black and white here as to whether GZ can establish such an affirmative defense. A prima facie case of murder is pretty easy to establish here - GZ doesn't dispute he shot TM and it's a fact that TM is dead. The question is whether GZ can establish he acted in self defense. Florida law prohibits criminal prosecution under these circumstances here unless there's probable cause that the use of lethal force in self defense was not justified. Here, I suspect it probably was, but it's by no means black and white.
In order to convict a defendant in Florida of Second-degree murder, the State of Florida must prove the following three elements beyond a reasonable doubt:
1. The victim is dead;
2. The death was caused by the criminal act of the defendant;
3. There was an unlawful killing of the victim by an act imminently dangerous to another and demonstrating a depraved mind without regard for human life.
We can agree that criterion #1 is met. Perhaps you can provide prima facie evidence the #2 and #3 are met? A corrupt prosecutor filed an inadequate and unethical petition that was accepted by what we now know is a judge found to be biased against GZ. There is no credible evidence that GZ committed a crime in killing TM; in fact, all the credible evidence points to the contrary. There is no evidence at all that GZ killed TM in a state of depravity with no regard for human life. The prosecutor and judge deprived GZ of justice because they fear the threat of a racist riot. So much for equal protection under the law in Floriduh.
I also don't think it's 100% clear that the force was life threatening. Just because a head wound can theoretically be lethal doesn't mean that each and every head wound justifies the use of deadly force. GZ had some cuts on his head and there was some blood, but anyone who's had or seen head wounds in a fight knows that even the smallest cut on the head will put out a lot of blood, especially during a fight when your heart rate is up and the blood is pumping full force. I'm a bit suspect that a broken nose and a few minor cuts can (or should) rise to the level of justifying lethal force. Now, if they can establish he was slamming his head into the ground or something along those lines (as opposed to his head scraped the ground during the scuffle), he would certainly have a stronger case.
How many bone-breaking, head wound-creating blows to the head are you willing to absorb before concluding either that you are under threat of death or grievous bodily harm? With all due respect, you are free to absorb as many as you like, but if you respond with a number greater than one, I must conclude that your genetic fitness is rather low.
Don't forget that GZ yelled for help for more than 40 sec, and only remembered that he was armed whem TM noticed his pistol, informed GZ that he was going to die, and attempted to steal his weapon. Are you also willing to give a bad guy who informs you he intends to kill you your carry weapon? Feel free to be generous and turn the other cheek (for the final time), but even Floriduh law doesn't require that, Castle Doctrine or not.
In any event, I fail to see how this case is black and white (or how invoking the Constitution is at all relevant). Hm, bad analogy - I meant that figuratively, not literally. 
The case is B&W because there is insufficient evidence to charge GZ with murder. Because of fear of or sympathies with the riotous racists, the prosecutor and judge have ignored the law and the facts. How long the injustice system will persecute GZ remains to be seen. As has been noted in this thread, there are good reasons to question the competence of GZ's attorney, which doesn't bode well for either GZ or ultimately the law (and thus Floriduh society) to prevail.
I mentioned the Constitution because it, along with many of this country's laws (at all levels), are frequently ignored -- we are no longer a nation of laws, but of men. GZ's persecution demonstrates this perfectly -- his individual rights are being sacrificed to appease the riotous masses consisting of racists, anti-gunners, and bleeding-heart progressives.
Now gosh darn it, please tell me what finish you have on that good-looking CZ 82 of yours. I have one on the way and am pondering how to refinish it if it needs refinishing.