>But what if your coworker likes attending KKK rallies and you're African-American? Or your co-worker is out there on the weekend holding signs that say "Death to Gays" and you just happen to be gay?

Yes yes, we can all dream up the very worst case scenario and other outliers. As someone else pointed out, companies generally have contract clauses that even govern social media whereby if you represent the company poorly you'll be fired. I'm sure that easily extends to your proposed sign waving homophobe.

The point the GP made was that most people have a lot more in common than they differ on, but in this hyper-politicized era those differences have been magnified to become an issue of pure division and likely shouldn't be brought into work with you.