I think that what's different about the Internet is scale. On the Internet, you can find a group of people to validate whatever fringe theory you want - and with social networks, you can do this _extremely_ easily. When you do find these people, you treat it as validation ("See, I'm not the only one who thinks this!").

For most of human history, if you had a fringe idea, your community would be extremely skeptical until you came up with something to convince them - or, more likely, concluded "huh, no-one else thinks this, I must be wrong" and veered back into the mainstream.

Even in the days _just before_ the internet, with pervasive newspapers and TV, your 'circle of validation' would've been _much_ smaller.