Jerks like this guy do more to skew public opinion against gun owners and SYG laws than all of the anti gun activists put together.
SYG laws are in my opinion - and probably the opinions of most informed people - very reasonable. However, when public opinion starts associating SYG with "if you have a gun you can use it to win a fight" I think we'll find we have a much harder time getting them added to the books, or keeping them.
Sadly, in our public opinion driven political system, what people think usually trumps the truth.
Most people don't have a vested interest in gun rights, and don't bother to find out what SYG laws actually do. They believe what they see on the news. When we have cases like this guy (and the one-who-shall-not-be-named in FL), people are going to start to think that this is what SYG laws are about.
And when that happens who would blame them for voting against them? Frankly, I would vote against any law that would actually make this guys actions legal.