Simply put: People who go through the effort of commenting under a thread tend to follow the lead of the post in question. Whether it be taking it in the same or the opposite direction, the OP is the one who dictates the flow. Exceptions to this include ‘hot button’ topics where people have pre-formed opinions and when a community in general is predisposed to being fiery vs cool-headed.
This is why having a figurative canary and/or persistent ‘rent-lowering gunshots’ in place on a site is a good thing. The less advertiser friendly a place is, the better, and if that thing keeping advertisers out is the content itself then I’m all for helping that along a bit.