SYG is a reminder to the state that if someone is justified in shooting an another person, retreat was not a viable option.
Leftists don’t like subjects who can fight back.
If it had been a fact that Zimmerman broke Martin's nose when they first met, Zimmerman would not have been protected by the claim of self defense.
What stand your ground laws really do is restrict the over zealous prosecutor, in effect telling him “hands off”.