[phpisthebest]

Easy, both are trying to enforce their view of culture on the other via law and other government regulation.

The right is most seen on this in the modern era Womens Rights, Schools, Gay Marriage, etc

The left is most seen on this with Speech Codes around "Hate Speech" and Pronouns, in Employment Regulations, in Equity Regulation (enforced by law not market) ,etc

[freejazz]

But that's not a monoculture - those are two, very different cultures, actively competing with each other

[phpisthebest]

No that is 2 very different mono-culture attempting to eliminate the other

You seem to believe that because 2 cultures exist it is "multicultural" but that is not the reality, "multicultural" would be accepting the other culture as equally as valid as your own, tolerating their existence in a legal and market framework (i.e willing to do business with them, and not use government power to make their culture illegal)

What we have today is 2 cultures attempt each attempting to banish the other both using markets, and using governments.

[freejazz]

I think that's a vast overdramatization based upon reading the most fringe elements into everything else. The reality is the vast majority of people exist well within the edges and aren't anywhere near as fatalistic as you describe