It's a department at a company. You're not allowed to say that 'people of ethnicity X will never be given a leadership position'. That's blatant racism.
Do white-passing gay people not get to have a say in diversity issues?
I really don't like this trend of painting everyone with white-ish skin as a homogenous oppressor class. It's pretty clear to me that a diversity department that explicitly bans white people from leadership positions will not represent my interests if I am discriminated against.
Not wanting to be an ally unless you're allowed to be in charge is a pretty perfect illustration of why the slide exists.