The world's leading democracy, the U.S., is populated almost entirely by immigrants from non-democratic parts of the world and their decedents. With every wave of immigration, the claims are the same: They don't share our values, they won't assimilate, etc. It goes back to German immigrants around the time of the American Revolution (Ben Franklin had some particularly harsh words for them), and then Irish, Italian, Chinese, Eastern European, Latino, Catholic (Papists!), Muslim, Jewish, etc. etc.
The results never seem to match the theory; the current democracy and institutions of the U.S. are built by those people. Democracy means faith in governance by the people, and the very good news is that it works out very well relative to other forms of government.
Franklin on Germans: “A Colony of Aliens, who will shortly be so numerous as to Germanize us instead of our Anglifying them and will never adopt our Language or Customs any more than they can acquire our Complexion.” [1] Boy was he right, Freunde.
[1] https://immigrantarchiveproject.org/brief-history-anti-immig...
[0] https://qz.com/904933/a-history-of-american-anti-immigrant-b...
I prefer other forms of governance to democracy, such as Futarchy and certian forms of meritocracy in which standardized testing and sortiton are combined. One thing radical open borders would do is bring in an era of competition in governance, as for the first time there would be significant competition for citizens. Overall it is a good idea, but those who believe in the welfare state have little choice but to shun it.