Multicultural versus monocultural societies and countries

[Montmorency]

I agree, in principle.

However, monoculture is impossible without dramatic alterations (likely engineered) to the cognitive structure of the human brain.

Simplest answer: hive mind.

What nasty stuff happening in mostly monocultural countries happen considerably less often or never at all in multicultural countries?

I'm not going to bother with catching up in the Ukraine thread, but the example you used in your post is an exemplar of multiculturalism like a suicidal person is the picture of health.

In the interim, therefore, the embrace of multiculturalism is far less harmful than attempts to impose some formulated culture.