The polarisation is actually a good thing. As long as it's about stuff that doesn't matter for the normal economic activity. If they can still work with each other and live in mixed communities it's all fine.

They can always hope that their side will be on top in few years and restrain themselves. Such polarisation is no more dangerous than polarisation around sports teams.

And channeling and managing people's hatered is very important for stability. Otherwise it could be directed towards system of power as a whole, or the rich, or some ethnic group.