Calling it a global population collapse ends up sounding like a dog whistle.

It isn't immoral nor wrong, it's dumb though. Culture isn't some static stuff 'we do and have always done'. Most of the stuff we call 'culture', including food, is often at most 150 year old, barring a few very rare exceptions. We assign random characters traits to culture too, but it's funny because everyone ends up with the same ones.

Culture evolve with how we live anyway, and you cannot really 'preserve' a culture that didn't exist 70 years before and will be different in 50 years anyways. What people really mean by 'preserving our culture' really is 'preserving our heritage'. That will be done as long as no 3rd world war happens.

Go forth and multiply; no one is stopping you. The issue is when you take your own obsession with preserving your culture and try to turn it into a justification for running roughshod over others.