Shooting someone, even when justified (not specific to Zimmerman/Martin), has massive consequences for the shooter. I'm always appalled when I hear people say that if someone broke into their home they would kill them. They talk about it like they get a free pass to take someone's life. First, that's not what your rights are. Your right is to defend yourself. Seldom do I hear people talk about using deadly force as a means to self-defense. Usually they talk about it as a means to kill. Bragging about the caliber or ammo type of their weapon and how it would be sure to kill a person dead. Worse is when they say things like "two in the chest one in the head" as if to put the point on it that the goal is not to stop the threat but to kill a scumbag.
What I think they are entirely failing to realize is that regardless of their fantasies, they are not stone cold killers. The act of killing another human being will likely leave them severely traumatized. The act may be called into question, especially if they went beyond self defense and sought to make sure the person was dead, and they'll be defending them self against serious legal action. Their life will almost certainly not just return to normal even if the killing was justified.
Zimmerman was having marital problems before he killed Martin. His wife seems to have felt some sense of duty to stand by her man during his trial, but that's over now. Are Zimmerman's actions evidence that he's always been prone to violence and aggression? Or, are his actions evidence of the strain the using deadly force puts on a person coupled with the strain of a failed marriage? I don't think we can say.
What I can say, though, is that it is far better to use the least amount of force necessary to defend yourself than to seek out confrontations and use the maximum amount of force or equip yourself in a way that makes any use of force likely to be deadly.