So empires are good now?

Etruscans WERE the ancestors of the  Romans, they weren't "a nation" within the Roman Empire. The Romans admired Greek culture and adopted many of its features willingly as their own, just as they adopted the good parts of many of the cultures around them. That's what empires do. 

The British imported goods and ideas from all over their empire too, as did other European countries.  So did  Canada. 

You are praising assimilation, i.e. the melting pot, not multiculturalism, and I agree. We were doing fine as a melting pot, adopting the best of all the different cultures of the world, into what was a basically British framework.

The modern conception of multiculturalism is very different, it is of autonomous, parallel cultures that live according to very different principles, and otherwise ignore each other. That is what many object to.