More whataboutery. Would it be acceptable to say it about any other race? Actually, in the context, yes, I think it absolutely would.
If white people were being persecuted and systematically exterminated, then of course it would be racist to suggest that I didn't care if they died out. But that is not the scenario that we are facing here - not remotely.
And while white people might technically be a global minority, they are still a dominant force in the world and they are not actually disadvantaged by being a minority in the way that other minorities have been disadvataged through history. Quite the contrary.
So, if the relative proportion of white people is decreasing simply because white people themselves are choosing to have fewer children - a trend observed in educated women across the globe regardless of ethnicity - and/or because they are choosing to reproduce with partners who happen not to be white, then why would you think that was a problem? And why do you think I should care about it?
Can you explain exactly why you think it would be racist for me, as a white woman, to feel unconcerned about the choices that white people are making for themselves? Please try to explain this without trying to argue that it would be racist if you said it about another race, because that simply stand up to scrutiny.
But for the avoidance of any doubt, if black women were choosing to have fewer children for similar reasons, and/or if black people were choosing to have more mixed race children within the context of interracial relationships, then I would not care about that either.
I think it's entirely right that people should be free to make choices about their own lives, rather than feeling under some sort of bizarre pressure to reproduce simply in order to somehow sustain a race. Race is a social construct in any case.
Of course, it is legitimate to have concerns about the declining birthrate and how we are all going to support our ageing populations in the future. But that is a separate conversation entirely and has nothing to do with skin colour.