With all due respect, jetson, and speaking as someone who doesn't own (never mind carry) a gun, the reasoning you are putting forward here is flawed. I have self-defense training that would allow me to kill a person with my bare hands - the purpose of those techniques is to kill someone. Does that mean that, by having learned them, I have no position to stand on? I 'carry' them around with me all the time, since I'm trained in them.
That is the fault in your logic. A person carrying a gun is responsible for the use to which they put it, as is anyone who knows or has something that is potentially lethal. But that does not mean that when they 'carry' it, they intend to go out and kill people with it. Indeed, I would much prefer never to have to use techniques like that against another person. But the time may come when I have to, to protect myself or someone else.
If I had someone on top of me, beating my head into the ground (or into a concrete sidewalk), and I retaliated, killing them, I'd be responsible for their death. But the fact of the matter is that self-defense training is fundamentally about knowing how to act as forcefully as possible in order to defend yourself - and then putting restraints on that forcefulness so you don't use it unless it's necessary and you use no more of it than necessary.
And it's certainly true that Martin did not deserve to die. But he could have made better choices as well. Simply going into his house and calling the police, for example, rather than hanging around outside for whatever reason.