I hold a Concealed Handgun Permit issued by the state of Virginia, and my permit is recognized by the state of Florida.
I would like to address some of these points from my own perspective, experience, and instruction.
"Stand your ground" laws allow you to meet deadly force with deadly force. They don't allow the killing of unarmed persons. According to police, the kid was unarmed.
"Deadly force" isn't defined simply whether someone is armed or unarmed.
Whether that's just an assumption, a misunderstanding mostly attributed by the media, or romanticizing an old cowboy code, judicially it's just not true.
"Deadly force" is governed almost solely by the "reasonable man (person)" doctrine.
For example, in Virginia, "deadly force" is justified not only to protect ones self, but can be applied to protect ANOTHER person IF that person is in a situation that is potentially life threatening.
Some examples of an application of deadly force against an "unarmed" threat would be if an assailant had another individual in a chokehold, or was kicking a prone individual in the head, or even giving the posture or indication of about to kick a person in the head.
Pummeling an individual about the head with fists could also be interpreted as "life threatening", as real life is very unlike hollywood films, many persons die each year from simple fistfights, even an alarming number from just one hit to the head.
Looks like you only have to "prove" you "felt" your life was in danger to get away with murder in FL.
Practically every state in the union requires in some wording or another that an individual is to "believe" their life is in imminent threat in order to justify lethal force.
In many states it is also stipulated that they must BOTH "believe" their life is in imminent danger AND that they must exhaust all avenues of escape before resorting to lethal force.
"Castle doctrine" states remove the latter requirement about exhausting all avenues of escape, thus the "stand your ground" wording.
This coupled with the principle of innocent until proven guilty, then yes, pretty much you just have to "feel" your life is in jeopardy to use lethal force.
"Murder" however, implies much more than merely self defense, and I wouldn't want to paint all self defense encounters with such a broad brush.
But I do believe in this case, Zimmerman's actions do suggest enough probable negligence, escalation, and even foreplanning to warrant charges.
And personally speaking, as a concealed handgun permit holder myself, I have zero interest in any vigilante or hothead or nutcase behaving in a reckless and dangerous manner under the banner of a CCW permit holder.
I hold myself to much, MUCH, higher standards, and expect other CCW permit holders to as well.
It is taught because it is drilled into student's heads that they should only use their weapons in self defense, therefore its a true statement.
It is true that in my CHP class, taught by members of local law enforcement and a former local commonwealth attorney by the way, it was stressed over and over about the liability and responsibility and legality of lethal force, and a weapon is to be brought to bear ONLY when all other options are exhausted (Virginia has no "castle doctrine" but legal precedence in the form of a grand jury inquiry has historically aligned categorically with castle doctrine interpretation).
Someone going through such a course, who was bent on lying and trying to justify a bad decision and application of lethal force, particularly with no witness, could easily know EXACTLY what to say to minimize suspicion and liability.