The point of professionalism is to create a safe space, where people can work together to achieve things without their personal, political, and religious differences getting in the way. Saying your coworker is evil and must be excluded from society is inherently unprofessional.

I can't tell you with a straight face that you should never in any circumstance be unprofessional. But the ability to have respectful relationships across the aisle is incredibly valuable, and you'd better be sure it's worth losing. I think a lot of people don't even consider that cost.