I am saying employment is at will (in most US tech contracts) and an employer can terminate your contract for any reason. "Anything goes" = there's no set standards of proof
OK. Should "anything go", or is there a limit to how low the burden of proof should go?
That is not legally the case in at least some countries.
IANAL but my understanding is that employer can terminate you for no reason (as in not giving a reason). But if an employer fires you for cause and that cause is unfounded they can be sued for wrongful termination.
This handy list suggests you have a claim if you report you were harassed and your company fires you (retaliation), but not if you are fired after someone falsely accuses you of harassment.