For one, imo, George obviously wasn't concerned about his own safety, but that of his neighbors and, two, in connection with your earlier post, he did call the police.
Imo, it's all about the context. It is established that there were recent break-ins in the community which are known to have been perpetrated by young men, the majority of whom were black. George had recently assisted a woman whose home was broken into by this same group of criminals while she was in the home with an infant. That woman had to hide with the baby, most certainly praying for her and her child's life the entire time, and George was aware of this and had assisted her. These same criminals or "a&%holes" (personally, I think the shoe more than fits) did, in fact, "get away," as they fled out her back door just as the police arrived.
If I were a man, particularly a man who was a neighbor involved in assisting that woman and part of the NW, I would have done anything in my power to make sure that another incident just like that didn't happen again. Because I'm a woman, I'm not sure I would have followed Trayvon, but I'm feisty and I might have. In any case, if I knew that another woman and her baby in my neighborhood had gone through that, I would have done my very best to make sure I knew where this person was until the police arrived, this time. And if that meant following the person I was suspicious of, then I would have.
It was completely fortuitous that George was wrong about Trayvon. Imo, he had every right to be suspicious and I would have been, as well. Very much so, in fact.
For those reasons, I believe that what George did up to the moment of confrontation is, potentially, completely reasonable. It's what happened in those last seconds that matters to me.
The question in my mind about those last seconds is this. Both George and Trayvon's girl friend agree that Trayvon asked George why he was following and that George asked Trayvon what he was doing there. Why did Trayvon not simply say, I'm staying with my Dad over at *advertiser censored* address. Even if he thought George was going for a gun rather than his cell during that conversation (which I don't think has been established and I'm not sure I believe, anyway) wouldn't a reasonable reaction be "Wait! Dude!, my dad's gf lives here -- right over there. I'm just on my way home!!!"