Zimmerman was on public property. He was a neighborhood-watchmen. He wasn't hurting nobody (not even Trayvon) by watching him. If Trayvon didn't like it, he could simply leave.
No altercation is justified.
If it is true that Trayvon tried to grab Zimmerman's gun, then the results (the fatality) are justified.
Not so simple when a crazed racist is following you.
"When walking in open territory, bother no one". Right Atlas?
I've dealt with crazed racists. Stupid but not dangerous. Beliefs do not make someone a threat. Only actions do.
Thoughts being a crime -- that's a scary precedent. It's why I don't believe in "hate crimes". A crime is a crime. A thought is a thought.
We should never prosecute somebody for their beliefs even if they are racist.