"Like the thriving, polite, constructive exchange of ideas that took place on /r/the_donald for instance?"

I have never visited that subreddit, but since the rest of the world, downvote button or not, was also not really involved in a constructive exchange of ideas on that topic - I do not see the point here. Emotional topics are hard to discuss, if the people involved use it to vent out emotions and to evangelize.