Company interest is king. If the person's skill set and connections are a valuable asset to the company, then his personal views and traits shouldn't be something to be concerned about. Maybe tell him to dial down the preaching and focus on the job. Measure his value through what he does and not what he says.

On the side note I think this topic is quite frightening in some way. We reached a point where a company, or employee is not going to be measured by the product or value they make, but what political views they represent. Soon we are going to have political questions on an interview. The companies will police their employees what they say and what they do in social circles. Workplaces become political echo chambers.

Also like how you just state that he is "politically incorrect", making your views the only correct ones. Not different, but incorrect.

Talking about double standards.