Here is the relevant portion of the Florida statues on this: 776.012 Use of force in defense of person.—A person is justified in using force, except deadly force, against another when and to the extent that the person reasonably believes that such conduct is necessary to defend himself or herself or another against the other’s imminent use of unlawful force. However, a person is justified in the use of deadly force and does not have a duty to retreat if:
(1) He or she reasonably believes that such force is necessary to prevent imminent death or great bodily harm to himself or herself or another or to prevent the imminent commission of a forcible felony; or
(2) Under those circumstances permitted pursuant to s. 776.013.
The rest can be read here: http://www.leg.state.fl.us/statutes/index.cfm?App_.../0776/0776.html
Myself, I find it hard to argue against a person's right to defend themselves--especially when faced with "imminent death of great bodily harm to himself or herself or another or to prevent the imminent commission of a forcible felony."
The main problem with this law is that there are circumstances where the jury may have to be psychic to determine whether the person using such foce "reasonably believes" it is necessary. Dunn's case seems to be one of these. Obviously it doesn't seem to be reasonable for a guy to get off for shooting up a bunch of teenagers in an SUV based on his contention that he thought he saw a shotgun. What with no such gun being found, it seems very possible that the gun was either Dunn's imagination, or that he way lying.
Now it appears that Dunn has been convicted to serve 60 years for attempted murder. If I understand what I'm reading right, he will face trial for murder again, due to a mistrial, so I assume there is still a chance of a murder conviction. If the facts are as they appear to be, it seems to me he should be convicted.
So I would say that, while there's nothing wrong with the law allowing people to defend themselves in life-threatening circumstances, they had darn well better be able to prove in court that it really was reasonable to believe "that such force is necessary to prevent imminent death or great bodily harm, etc." I think the courts need to interpret the law in such a way that the proof needs to be pretty solid. Claims of seeing a gun, when no such gun is found, don't seem very solid to me.