Multiculturalism was all based on a grand lie from post WW1 era elites, and is easily disproved by published, peer-reviewed scientific studies.
Highly suggested video below that includes many of the studies.
A few years ago, I became really fascinated by the origins of multiculturalism as an ideology (and movement) --- considering it seemingly came out of nowhere in the 20th century, became pushed in all parts of mass western culture, but has incredibly murky origins. Almost every other ideology you can easily trace the roots of (and has known founder) -- but multiculturalism is much more murky.
And most importantly, multiculturalism is only selectively pushed in western countries who make up less than 20% of the global population. Why are the elites who push multiculturalism not telling Thais / Nigerians / Bolivians / Fijians to become multicultural?