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Diversity and the acceptance of diversity is a good thing in general. For example, companies like Apple, Google, Microsoft, Intel, Amazon, and many others hire talent from all over the world, because talent is found all over the world.
I think what you're talking about, though, is "forced diversity for the sake of diversity", which is a policy pushed by the left in order to create more people who are dependent on the government, and thus who will keep voting in the lefties who promise them your tax dollars. In that case, diversity is just a pretext to try to give the lefties a "politically correct shield" - it allows them to make the argument that if you oppose large-scale immigration - especially of low-skilled workers - that you must be racist. That ignores the other reasons why people oppose large-scale, low-skill immigration, but the lefties have figured out that calling people racists - even when everyone knows it's a lie - makes people uncomfortable and often causes them to abandon their argument in order not to appear racist.
If immigrants could not vote until they had lived in the US for 20 years, the Democrats would be arguing FOR the border wall - and probably a minefield and airstrikes - because their only actual reason for wanting open immigration would be gone.