Since when did anyone ever expect due process when being fired? This is a world where you can be fired for showing up 30 seconds late because of a road closure.
So it seems like we agree that this particular aspect (snap firings) of the USA sucks. So why is this _not_ the one to fight? If we both think the core issue is a problem, it doesn't seem intellectually honest for one of us to say that a specific instance of that general concept doesn't count because the dude at the heart of it is scummy.
If you can build a strong and convincing argument that his termination is wrong, it'd be trivial to apply that argument to the case of the fast food worker. And therefore have a better shot at improving their lot.