I was under the impression that in the past, viewers and readers tended to self-select for television, radio, and newspapers that match the opinions they wanted

I was under the impression that in the past, viewers and readers tended to self-select for television, radio, and newspapers that match the opinions they wanted to read. "Old media" had editorial decisions and tone that affected collective decision-making. "A small number of zealots ... bias vote outcomes" sounds uncannily like the narrative in the song "Non-Stop" from Hamilton (spoiler: "he wrote the other fifty-one" essays). So do social networks make this effect bigger? Smaller? Allow it to happen internationally? That is not to say that a new medium has no impact on collective decision-making -- there are papers describing how the radio led Americans to elect people that sounded good, and the television led Americans to elect people that looked good. https://doi.org/10.1080/01439688800260171 https://doi.org/10.1080/01439688800260171