Companies are not relationships where once they're your ex they are never worth interacting with ever again. If you are doing good work and then HR pushes you out, then it is reasonable to sue the company to get them to pay you damages and then go back to doing what you were before with the protection that they won't do it again.

The point I tried to make was not that he should be resentful about being kicked out, but that he doesn't really care that Meta is unethical and endangers billions.

Even if nothing changes (the regulatory action is optional), he's happy to contribute (he insists, in fact). Even among people who don't want him there.