People dont want to have to go into a Warren, Bernie or any candidate thread if they trying to talk about the debate and current status of the general race. That doesnt make logical sense and that's what the two general topic threads are for. There were a bunch of people last night either at work, leaving work, or didnt watch but wanted to catch up on the debate discussion and potential jump in the discussion by quoting other people posts. Closing the threads cut off their participation. That's not right to do that to members.
On smaller forums this is how people rebel and leave sites. When discussion is cut off because it doesn't meet a mod's personal standard. As long as rules aren't being broken then discussion should be allowed to flow. If there are continuous bad actors then they are dealt with individually, but the whole section shouldn't have to suffer. That's not how members should be treated.
At this point in the primary, people are expected to be emotionally invested. People are expected to strongly disagree with each other. That should be a good thing, because it shows how passionate the members are about the candidates they support and the overall primary. Discussion may be mixed with arguments and some trolling, and some people may not like it, but during the course of political dialogue that's how people are going to express themselves especially with Iowa, New Hampshire being around the corner. I haven't see anything so outrageous that it warrants a whole thread to be closed.
As I said before, this kind of moderation encourages members to look elsewhere to seek the discussion they want to have. Moderation should always be done in the forum's interest. Not in personal interest. And if you think this actually is in the forum's best interest then clearly you miscalculated as you can see by the backlash.