I’m not Skald, but: obligation? No. Right? Yes. Unless you’re in a state where employment isn’t ‘at will,’ an employer can fire an employee for any reason at any time, except for specifically protected reasons like race, religion, sex, and the like, as ratatoskK noted earlier.
And while he isn’t under any obligation to act as (all that stuff), we all do things that we’re under no obligation to do, because we feel we should, or because we want to, or just for the hell of it.
Now specifically this:
Executioners carry out death sentences. I’d have a real problem with a private person, employer or not, doing that. I hope you realize that’s not what we’re talking about here.
And we all act as judges and juries in the ambit of our own lives. I know a guy who kept cheating on his (now estranged, soon to be ex-) wife. Or rather, I used to know him. I don’t have anything to do with him anymore. That’s how I roll. He didn’t break any laws, but I acted as judge and jury of the part of his life - his friendship with me - that was under my control.
What right did I have to act as judge and jury? Didn’t his wife punish him enough by finally giving him his walking papers? No; I just decided I didn’t want to have anything to do with him. My life, my choice. If I were his employer, it would be: my business, my choice.