> What I would have done is get them to define what each means by white supremacy in detail...then debate on the detail.

As a friendly piece of advice, this approach is going to get you fired from a few companies. If you're in a management position it could well get your company sued.

When someone comes to you and says they were victimised because of racism or sexism it's a good idea to ask them what happened, and what they'd like to do to put it right. You can then decide whether those are reasonable, and whether or not you are going to do anything.

But it's a terrible idea, once you've asked them what happened, to then say "but why is this racism?" and then to argue with them about whether it is or not.