So you would gamble your life on the fact that the suspicious person wasn't armed as well? :what:
If he was truly motivated to help LE, he would have followed from a safe distance in his car, and not become a liability.
Then how did Zimmerman end up outside his car? (riddle me that)
edit: And while we're talking what ifs, what would have happened had Martin been a couple years older and had also been carrying legally?
Would it not be safer to watch from inside a vehicle and call the police if you see something suspicious?
He left the safety of his vehicle in pursuit. That no longer is "watch".