I agree with that. The law penalizes aggression, and it penalizes escalation.
Adding some remarks - you said that Zimmerman would lose his right to self defense if he started the fight. You seem to be implying that he has a duty to retreat, since he (hypothetically, of course) started the fight. If he can't retreat because Martin has him physically restrained, the law is not going to hold him to discharge the duty to retreat. If you start a fight, and your opponent pins you, and your opponent then escalates by holding a knife to your throat, or smothering your with a plastic bag, etc., you are not held, by the law, to take "death" because you started a fist fight. You can't retreat. You can use deadly force in self defense if you are in fear for your life.
If you can't retreat, it doesn't apply.
"the person reasonably believes that he or she is in imminent danger of death or great bodily harm and that he or she has exhausted every reasonable means to escape such danger other than the use of force which is likely to cause death or great bodily harm to the assailant"