the week's U.S. shooting

Well, it's early; just Monday. More could happen, of course. But I always expect at least one per week anymore (aside from ongoing gang violence, which I don't think will ever end no matter what gun laws are). But today's was in a courthouse in Delaware (read it here).

Now, I'm confused about something - the people who absolutely oppose any further regulation on any weapons, even if it's just background checks and assault bans, tell us there won't be shootings in public buildings (and I'd say a courthouse is as public as a school, both are taxpayer supported) when there are armed guards there to prevent it. You know, the only thing that can stop a bad guy with a gun is a good guy with a gun, and all that guff. Yet, I'm pretty sure courthouses generally have armed officials on staff - in fact, the story mentioned officers who were hit, but wearing bulletproof vests. And these officials are, by and large, supposed to be "good guys."

So ... how did this happen? I'm mystified.