Correct. "At will" isn't quite the dystopian corporate nightmare some make it out to be. You can't just make up a reason. It has to be valid, and even if it is, it will be a headache for the legal department if there is even a hint that the person was targeted for being in a protected class. If it's proven the company fabricated the reason, well, you might as well name the company after person at that point.
That's why companies still go through an enormous amount of procedural and documentation hoops before they fire someone, including PIPs.
It doesn’t have to be valid. You can fire someone because you don’t like them, or for no reason at all.
You just can’t fire them for a prohibited reason, such as race, age over 40, sex, disability etc.
Needing a reason is more of a practical problem - every person is a member of at least two protected classes (everyone has a race and sex). If you have no reason for firing a person, it’s often pretty easy for them to argue it was really based on a protected characteristic.
No, there has to be a reason to determine unemployment benefit eligibility.
No smart company will ever put down "don't like them" or something more PC like, "culture misalignment." That's an invitation for legal issues. They're going to tie it back to performance as much as they can, and that takes time and effort.
That's why companies still go through an enormous amount of procedural and documentation hoops before they fire someone, including PIPs.