Earlier quoted context omitted.
Because political discussions are incredibly polarizing, specially these days, and once they are allowed they pulverize the company into factions that cannot work together until the more strident or powerful of these factions takes over and pushes everybody else out or into silence. And when this happens, you have an homogeneous political body as the gatekeeper to the worlds information. What could go wrong?
So the key to a diverse organization is not talking about politics? Seems unlikely.
Politics and religion are uniquely divisive subjects, and when you allow endless arguments about them, you create a rigid and hostile atmosphere that kills comity and intellectual collaboration. Everything becomes an argument about politics, and then activism, and than ostracism and purity spirals. It's a classic pattern.
So yes, you really should taboo political arguments if you don't want to drive away people with independent views.