My gut feeling is that "work" (as it we know it now) is pathological. The fact that it's considered best practice to separate work and friendships, says a lot about the nature of work. Our modern age conception of work is literally 'soulless'.
Then there's risks involved in exposing personal opinions to people at work. If you two have a falling out due to different political ideologies, religions, hobbies, etc., that can make continued work more difficult.
Finally, it has the potential to foster a workaholic culture at the job. Why leave work when your "family" is there? But when that is the norm of the company, workers can feel compelled to work ridiculous hours, like Japan's work culture.