I see what you're getting at, but I don't think "whataboutism" is the right term for that. Whataboutism would be like Facebook being criticized and someone resp

I see what you're getting at, but I don't think "whataboutism" is the right term for that. Whataboutism would be like Facebook being criticized and someone responding, "Yes but Apple does it too!" What you're describing seems like it's an example of how everything eventually reverts to the mean. In this case, the "mean" point of discussion for any topic is the subtopic most people are familiar with and have a strong opinion about. Controversial topics are much more engaging, which means threads about them attract more comments. In turn that surfaces more attention to them, from which it follows that on any given topic you're likely to see people slowly shift the discussion to the most familiar subtopic, which will generally be the most engaging (and thereby likely controversial) one. It's a feedback cycle which sustains a meme (in the linguistic sense of the word). A majority zeitgeist is formed around an idea which is thoroughly self-propagating, because every time a topic with any degree of relevancy pops up, the discussion shifts to the meme.