If the program merely existed, that would be one thing. But if the company is spending millions and talking about their dedication to increasing URM representation, that makes it clear that dissent is not welcome.
To go full Godwin, firing people for expressing outright fascist viewpoints is also anti-diversity: it's excluding fascists.
Basically, there's no way to have true diversity and inclusion for all viewpoints, because so many viewpoints are mutually incompatible. There's simply no way to reconcile the viewpoints of two people, one of whom is LGBT (or at least pro-LGBT rights) and one of whom thinks such people should be marched into death camps. This really goes for any kind of viewpoints; you can only accept so much diversity of opinion before you get into an irreconcilable conflict.
In normal polite society, we avoid this problem by simply forbidding discussion of certain topics in certain places. But that means people cannot feel safe expressing themselves fully in those places; there's simply no way to allow that as long as diversity is allowed.
who cares about their viewpoints? it's not even a slippery slope because it's just so absurd that people should be polite and respectful of genocidal ethno-nationalists. /shrug
You'll very quickly be sent for "re-education" if not downright fired.