Chrissie I understand the experience you have shared. However, being extra cautious of certain people and situations due to past experience is completely different to what happened here.
Zimmerman was not being extra cautious he had decided based on skin colour alone that Martin was guilty of something. He was not behaving cautiously, he hunted Martin down, ran after him when he tried to flee. He was that determined to get his criminal...based on nothing other than the colour of Martin's skin.
Imagine you were walking home alone on a dark wet night and a man started following you. First of all in his car, slowly following behind you. Then when you were so scared you ran to try and get away, he got out of his car and chased after you, whilst on the phone to the police accusing you of being a criminal. Are you saying this would be perfectly acceptable if the man in question had experienced crime at the hands of someone with the same skin colour as you?
Not because he thought you looked like anyone specifically, not because you were doing anything remotely suspicious but just because of the colour of your skin.