I've never seen this. Can you link some examples?
And while people will surely respond to this post with "Ha, got him! He can't link to a specific example!", I don't believe it's a reasonable expectation of me to catalogue the thousands of comments I read on this website.
Searching for "US demographics collection nationalists" finds one result (your comment above - and presumably soon this one): https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
I tried "US data collection nationalists" but that only found one page of results none of which supported your assertion: https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
Do you have a better set of search terms?
The closest I've found is [1] which is a downvoted comment saying:
> Census data indicate White population has shrunk since 2010
Why is this the first bullet point? Why a focus on White people? Why do you care HN?
The only other place I see stuff like this is when it’s used as an alt-right talking point, or by white-supremacist mass-shooters who write about ‘The Great Replacement’ [1]
So that isn't even arguing against collection of stats. But it's the closest I've been able to find.
Perhaps you are misremembering?