I think the way you feel about this (which I agree with) is probably down to how seriously people take these different types of appropriation, though, not that one is 'worse' than the other. At present, we don't accept cultural appropriation as a basis for someone 'changing nationality' for example. If we did, I would find that just as scary and bad as people thinking we can change sex. At the moment it doesn't impact your life for someone to appropriate your culture, but it would start to impact your life if tomorrow we decided anyone can identify as whatever race or nationality they like, and start taking up opportunities for that race/nationality, access spaces for that group, etc etc. Which is what is happening now with sex appropriation. And this comes back to what I said earlier - why is sex appropriation taken so seriously and considered acceptable when the same would not be said for any other protected characteristic? It makes no sense.