It certainly depends on employee's financial and social circumstances and the industry specifics, but it still begs a question if it's worth working for an arrogant asshole that could fire someone for a over a bad mood. Even if there's a law that says that they can't, one must be in quite dire circumstances to cling to a job where they are mistreated.

This said, I totally recognize I'm quite privileged in regard that the industry I'm working in, where business tend to generally value people and such senseless human resource management is typically misaligned with both employee and employers goals (putting it simple, being an asshole doesn't bring any profits). In such circumstances, my personal perception of at-will employment is positive - it makes sense to me that we (employee and employer) cooperate because we like each other, and there's nothing that binds us but our will for a mutually beneficial relationship.

Yet, unfortunately, I know this is not the case for many people but I have no idea what could to be done to fix this. But I suspect that legal protections that prevent firing people at-will are not helping the core issue here.