I believe the outrage is not about how good this particular 'martyr' is but because he was found guilty by the same system that decides when a person can reasonably use deadly force in a state that has laws specifically designed to 'stand your ground' and even then he was found guilty by a jury of his peers.
So with everything going for him he was still found guilty, so now someone can undo all of that just because they feel like it?. This spits in the face of the entire state and its judicial system.