Multiculturalism is hardly inevitable but for the current path of western nations wherein this very new idea has become sacrosanct and any aversion thereto is condemned as so much bigotry and xenophobia. Thus it is inevitable only so long as this twisted idea that any resistance to it is wickedness, hate, racism, etc., continues
What western nation exactly was calling out for multiculturalism prior to the massive and politically motivated changes in immigration laws and policies beginning primarily in the 1960's? And what benefit does it bring a society or single culture anyway? Multiculturalism, like its stepbrother "diversity" is a grand "strength" and "benefit" we are told - yet few can cite more than some simplistic tripe about ethnic food choices as a plus of any kind! The only people who benfit from multiculturalism are the "multis" and those who either exploit them, make money championing them, or extort the natives peddling them all manner of clap-trap about the supposed glories of "Diversity" etc. The classic self-fulfilling prophecy - Diversity only became fashionable, desirable after the fact!!
I find various peoples from around the globe interesting culturally and individually - but I don't see the wisdom of importing them by the tens and tens of thousands into every western nation on the earth for the sake of this multiculti experiment. The greater the mix the greater the strife or likelihood thereof. And given that the "payoff" is either nebulous at best or simply unknown - why take the risk?