I think scale matters, though. In the 1500s (through much of the 1900s, even), most people were still mainly exposed to the viewpoints of people and groups who were physically local to them. Your local newspaper and (more recently) local TV news was a product of local attitudes and opinions. Certainly all of those people were not a member of your "tribe", but many were, and there were limits as to how far off the beaten path you could go.
If you had some wacky, non-mainstream ideas, you self-moderated, because you knew most of the people around you didn't have those ideas, and you'd suffer social consequences if you kept bringing them up and shouting them from the rooftops. Even if you decided you'd still like to do some rooftop-shouting, your reach was incredibly limited, and most people would just ignore you.
Today you can be exposed to viewpoints from every culture and every walk of life, usually with limited enough context that you'll never get the full picture of what these other people are about. If you have crazy ideas, no matter how crazy, you can find a scattered, distributed group of people who think like you do, and that will teach you that it's ok to believe -- and scream about -- things that are false, because other people in the world agree with you. And the dominant media platforms on the internet know that controversy drives page views more than anything else, so they amplify this sort of thing.
If you had some wacky, non-mainstream ideas, you self-moderated, because you knew most of the people around you didn't have those ideas, and you'd suffer social consequences if you kept bringing them up and shouting them from the rooftops. Even if you decided you'd still like to do some rooftop-shouting, your reach was incredibly limited, and most people would just ignore you.
Today you can be exposed to viewpoints from every culture and every walk of life, usually with limited enough context that you'll never get the full picture of what these other people are about. If you have crazy ideas, no matter how crazy, you can find a scattered, distributed group of people who think like you do, and that will teach you that it's ok to believe -- and scream about -- things that are false, because other people in the world agree with you. And the dominant media platforms on the internet know that controversy drives page views more than anything else, so they amplify this sort of thing.