People who show up for political debate generally do so with knives drawn; you hear from the loudest people with the most solidified views, and the stuff that rises to the top is playing to the crowd instead of engaging in extended discussions. But in a rec sports team, a movie club, or a tech forum, people aren't grouped by viewpoint and vitriolic arguments are a distraction from the original cause. So those places seem to breed conversations where people take the time to hear one another and avoid breaking down into pure tribalism.
Another way of looking at it is that in that context, they are interacting as fellow members of their "rec team tribe" rather than as members of competing political tribes. (which they may also be a part of)
I feel like at less than ~ 3:1 "citizens":stranger ratios, any conversation spirals down. Because someone inevitably takes the bait, responds to stupidity, and there goes the thread.