The gun grabbers will give you one of two answers. they will either claim that this case is an irrelevant anecdote. Or they will accuse they gun owner of murdering the "poor criminal who was starting to turn his life around.
But in the end, it is about power. Anti-gun people tend to be statists. And owning guns meaning you are not wholy dependant on the state. And authoritarians despise people like that...