America under the influence of free market fundamentalism de-regulated itself into this.
First it was the FCC's revocation of the Fairness Doctrine, which had mandated balance on the airwaves for political speech. Rush Limbaugh became a nationwide radio syndication value proposition not long after, because it became easier to segment audiences by ideology, which in turn promoted polarization.
Then came Section 230 of the Communications Decency Act, which released internet platforms and ISPs from liability for the content that users published. The "decency" part is long gone -- the anti-pornography parts were revoked. What was left is the free pass for libel.
It's virtually impossible to propagate a conspiracy theory without lying publicly about somebody. These two deregulations made character assassination cheaper, easier, safer, and more profitable.
Supposedly, a "marketplace for ideas" would prevent poorer quality ideas. But that "marketplace" metaphor was framed in a Supreme Court judgment before radio emerged. The thing about markets is that they work when buying costs you something. In that era, the price was reading, which allows time to pause and think--a cost in time and effort. Audio and video makes political communications much more entertaining than reading -- and less likely to evoke thought as opposed to feeling.
Freedom of speech was constitutionally guaranteed back when audience sizes were limited to how far your voice could carry. Freedom of the press was defined back when propagation of the printed word was relatively expensive, and so was the education that allowed a community opinion leader to become influential through reading and careful thought. Electronic mass communication is not, in their original senses, either speech or the press. And it tilted the "market" playing field toward propagandists. Hitler, Mussolini, and the Japanese militarists all surfed to power on the airwaves.
America had some countermeasures against the weaponization of electronic mass communications. Unfortunately, greed and power-lust won the day. And they are still winning. As they have before. Don't say "it can't happen here" if you don't understand what happened over there.
