>Balkanization is bad for any nation.

Balkanization means "to break up". This is not multiculturalism but just the opposite.

>Stripping a nation of its commonly shared cultural identity is a great way to weaken it.

There is no way to prove this statement. I challenge you to find academic work to support this and examples demonstrating this.

> Just look at you guys with your separatist movement where it's illegal to post signs in English only in Quebec.

Off topic. This has nothing to do with multi-culturalism. In fact it is just the opposite.