I'm not convinced of this rebuttal. The problem is that these systems tend only to improve serendipity within the comfort zone. Greg's One True Scotsman argumen

I'm not convinced of this rebuttal. The problem is that these systems tend only to improve serendipity within the comfort zone. Greg's One True Scotsman argument that a "well-designed" system would of course be better is not convincing either. Naive systems optimize for things you already like, or variations on things you already like. The system doesn't need to present a broad array of ideas. Presenting you with something that causes a strong negative reaction is considered a bad thing. Newspapers have the same problem to a lesser degree: I know folk who read the Weekly Standard and who wouldn't touch the NYT with a bargepole, and vice versa. We just have many more, smaller echo chambers. People will always have to make the conscious effort to give strange views a fair hearing.