The problem with George Zimmerman was that he was a threat to his community. It seems strange to me to just blame "stand your ground" laws on precisely the people that are a threat to the community.
Anyway, can you imagine if more robberies were greeted with this? You don't think that would change behavior? Be serious.
So what do you do with the Zimmermans of the world? You do exactly what we're doing: you prosecute them. You let the justice system determine if their actions were appropriate. The way I see it, Zimmerman is a violent thug. Do we even know if he knew about "stand your ground"? It's likely he would have carried a gun with him and used it overzealously on neighborhood watch whether that particular law was in place or not. We have at least two tools to protect ourselves from violent thugs: guns and the justice system. Trayvon Martin didn't have the former, so unfortunately in that case we have to resort to the latter. Tragic things like that happen. But they don't validate the argument that because thugs carry guns good people shouldn't.