Well I think it’s less about preserving culture in some static form, and more about having everyone on the same page, and working towards the same goals. That doesn’t seem reasonable?

>that doesn’t seem reasonable?

No not really. For starters, who determines what is the “true” culture or what the goals even are?

When does that ever happen?

"Culture" is a very large and full bag. Some items in it are fundamental to maintenance of civilization, others are entirely superficial.

Civilizational: Respect for rights of minorities, rule of law rather than of the strong, willingness to work and pay taxes, valuing education.

Superficial: Cuisine, dress, artistic taste, ritual formalities of religion.

Few governments have had success splitting immigration policy priorities along these lines, though some have had the wisdom to at least try.

Gradual culture mutation is different from sudden culture importation. There is a narrow neighbourhood in the space of possible cultures that is reachable from any given culture in it, this is the space explored by ordinary mechanims of culture change like cultural exchange and new generations.

Mass immigration explores the space very differently, in a way that is sudden and discontinues.I think it's reasonable for people to worry that they're being replaced, because that's actually what's (more or less) happening.

> I think it's reasonable for people to worry that they're being replaced

My issue is the entitlement that goes hand in hand with this mentality. Everyone replaces someone. What makes me so special that I get to go, “oh no you don’t, all cultural change ends with me and my friends unless I specifically sanction the change”?

People made room for me, after all.