Even if you won in litigation you'd have to prove damages.

I'm not up on labor law but it's not clear to me that an at will employee can prove much in damages since the employer never promised not to fire them.

If I sign an employment contract I've likely already left a job for the sole reason of taking the job for which I've signed the employment contract. At the very least it seems to me as if ~2-4 weeks of the employees previous salary was lost when it could have been avoided.

Offers etc. are almost never “employment contracts” — in fact, every one I’ve ever received points out that it is not a contract, and that the relationship is at-will.

There’s no difference between rescinding an offer, and terminating the at-will relationship one second into the first day - except a bit more notice.

Honestly I don't see how that could be true. If you hire me and fire me on my first day for no reason I am pretty sure you could prove that there are significant damages, the implication being that you would not have left your job in the first place if Meta hadn't reached out to have you interview.

If we're talking contract law traditionally you only get damages that get you where you would have been if the contract wasn't breached.

Leaving your job caused you a lot of harm, but if Meta could have honored the contract and still cause you significant harm (i.e. fire you one second after you began work) that isn't Meta's problem. (There might be some exceptions to this in some state's that require good faith.)

That said that's traditional contract law, I don't know labor law.

In Denmark at least, employment is at will during probation, yet you cannot just fire someone on day one or rescind the signed contract, as that would be seen as signing the contract in bad faith in the first place.

I don’t know how the US sees this, but surprisingly often the law works one “what’s reasonable” rather than what’s the exact wording.