How insecure must a person be to revel in such imaginary victories?
Yes, I would be comfortable with that scenario. A person with bad intentions is decidedly unlikely going to sit with a gun in plain sight, where everyone can closely monitor his actions, and where he is most likely surrounded by people who are also armed (and I don't just mean a couple security guards or police). Criminals generally attack when they have the advantages.
There are exceptions, of course; criminals have ventured into places where people were packing, but they are remembered as being rather stupid.