If things are as you described it, then isn’t that fear rational? What you seem to be saying is that people should hope that things happen differently this time than it did in history. That seems like the irrational part.

No. Fear of a needle makes sense in the wild, but maintaining that same terror when a doctor uses one to administer medicine is irrational because the systemic context has changed.

Fearing historical population replacement ignores the fact that prehistoric societies lacked modern state mechanisms to integrate labor. When you treat modern economic migration like a prehistoric invasion, you end up building policies that actively destroy your own society to fight a ghost.

We are seeing the results of this irrationality right now in the agricultural sector. Because we are legislating based on prehistoric fear, the state is deploying unaccountable, militarized enforcement units and holding massive numbers of people in extrajudicial detention facilities stripped of congressional oversight. The consequence of treating a massive economic input as an ex-ante criminal invasion isn't a safer society. It's systemic self-sabotage. Local farming economies are being decimated, crops are rotting, and businesses are failing because the workforce is either locked up or terrified. Building a massive, authoritarian state apparatus to destroy your own labor supply and crush local economies isn't "rational self-preservation." It is an irrational panic that breaks the modern system in a futile attempt to solve a prehistoric problem.

It's exactly as rational as people hoarding toilet paper at the beginning of Covid.

Just because some behavior made sense in a prehistoric society doesn't mean it does in a modern one.

In history things such as slavery, marital rape, and honor killings were the norm.

In all places worth living we overcame those, and it was not something done irrationally.

Why should xenophobia, racism and such not follow the same path?