On the Fact that of the Nearly 50,000,000 Foreign-Born People Living In America, a Significant Majority of Them Have Come from Countries that Have a Lower Average IQ, a Higher Amount of Corruption, and a Lower Level of Economic Freedom - https://www.youtube.com/watch?v=NcMd92XqlKY&t=2603s

Look, I get it. These are delicate issues to deal with. But if you're looking for a reason as to why multiculturalism has been an abject failure wherever it's been tried (and you don't want to blame whites completely, have grave reservations pertaining to the magic soil and propositional nation hypotheses, etc.), this might be a good place to start.