This is how we can get away with saying it's "encouraged" while really making sure any meaningful counter-argument is "forbidden" at the same time.
That's not obvious to me at all. The parent said "Where we seem to find ourselves today..." which pretty clearly implies a universalist statement, and one that happens to be dead wrong.
Also, there used to be a political spectrum and not just "progressive" and "conservative": This is something completely different than left/right - a right-wing person can easily be a progressive about his right views, while a left-wing person can be conservative [or even reactionary] about his left views.
[Edit: Note, I'm a non-native speaker: Maybe this differentiation is different between English than in German?]
@core-question's reply under yours wasn't an indication that yours was unclear; it was just taking the conversation in a slightly different direction (which is normal).
What is true is that people who are beliefs much are out of far outside the norm for their workplace are discouraged. For example, if you're someone who believes that profit is theft, and you make that clear during work, it will probably have negative effects for you. Whether "conservatives" are the victim of this depends on their workplace and just what views they espouse.
So I shut up.
It requires that people avoid becoming excessively emotionally invested in the discussion; such that disagreements do not negatively impact their working relationships.
Small teams with good temperaments are easily capable of this. Large organisations tend to look for more definitive policies that can be easily laid out and enforced.
Mind that this rule even prevents discussing legitimate concerns about customers with your team mates.
There is a middle-ground between "talking about politics" is "encouraged" and "forbidden".