If you've ever been an online forum mod, or similar, you'll know that the larger the "board" gets, the more out of whack it gets. When a company, or forum, is small, and most people know each other, at least a bit, they tend to stay civil. Past some point, that goes out the window.
Not talking about politics is a good idea, but it's very hard to specify what is "politics" and what is not.