They're not discriminating based on their job. The guns were the problem. They said they'd be happy to serve them if they ditched the gunzz.
I think the restaurant owner is a moron, but that's not my call. Her place, her rules. This is one of those Voltaire-ish moments, where you might not agree with the other person but you'll defend their right to express their opinions.
In general, I like more freedom rather than less. Business owners are free to run their businesses as they see fit in my perfect world, so it would be hypocritical for me to say she should be compelled to serve anyone she doesn't want to serve. Now, if there are consequences of her choices? She better not bitch about them.