(which is the law in most, but not all states) is a travesty. Within the constraints of Federal anti-discrimination law, it allows dismissal for any reason - work-related or not, for no reason, or even for a reprehensible reason (i.e. refusing to cook the books when so instructed by the employer). Here is a very good explanation of the issues involved.

Note that firing for political affiliation is not considered discrimination within the meaning of Federal law.

At-will employment is a human-rights issue, not an economic one.

The fact is that what we're experiencing right now is a top-down disaster. -Paul Krugman