A commenter writes:
It’s very troubling that someone can be acquitted on the basis of a self-defense claim without the defense having the burden of proof to claim self-defense. I agree that a 12-person jury would be a good change of the law, but another would be to bring Florida’s self-defense laws in line with most other states’.
Who should bear the burden of proving or disproving self-defense in criminal cases, and by what quantum (preponderance of the evidence, clear and convincing evidence, or beyond a reasonable doubt), is an interesting question. But on this point, Florida law is precisely the same as in nearly all other states: In 49 of the 50 states [UPDATE: I would now say it's 48½], once the defense introduces any evidence of possible self-defense, the prosecution must disprove self-defense beyond a reasonable doubt.
This wasn’t always the rule. The English common law rule at the time of the Framing was that the defense must prove self-defense by a preponderance of the evidence, and Ohio still follows that rule; the Supreme Court has held (Martin v. Ohio (1987)) that placing this burden on the accused is constitutional. But to my knowledge, only Ohio still takes the view — all the other states do not. [See UPDATE below for one other state, Louisiana, in which some courts in some situations also take this view.]
Of course this doesn’t dispose of what the rule ought to be. One way of thinking about that policy question is that the nearly unanimous rule takes the view, “Better that 10 guilty killers go free than one person who killed in proper self-defense go to prison for a long time (or be executed).” The Ohio rule, which is also the historical Framing-era rule is, “It’s slightly worse for one guilty killer to go free than for one person who killed in proper self-defense to go to prison for a long time (or be executed).” And of course one can consider variations of these rules as one shifts the burden of proof, or sets a quantum of proof at some other place, such as clear and convincing evidence.
But if you’re focusing on what is the view in “most other states” on the burden and quantum of proof in self-defense cases, then you should note that Florida is entirely in line with that view.
UPDATE (July 30, 2013): It turns out that there’s one other state in which some courts follow the Ohio rule in some situations — Louisiana. The Louisiana Supreme Court made clear that it follows the majority rule in homicide cases, and some lower appellate courts do the same in non-homicide cases, but other appellate courts follow the Ohio rule in non-homicide cases, and the Louisiana Supreme Court has yet to resolve the conflict. See State v. Glover, 106 So. 3d 129, 137-38 (La. Ct. App. 2012) for more details.