I completely forgot about Nostradamus until this reminded me of it. He was having a bit of a moment in the mid '00s for this exact reason. Looking back, I can see that time period as an incubation period for the popular conspiracy mentality we see now. These sorts of ideas were being peddled everywhere, and were benign* enough to latch on to people without much life disruption. I wonder how much of this acted as a cognitive primer for the eruption into the mainstream of much harder conspiracy theories we see today.
* At the time your wonky conspiracy brained coworker would be sitting down saying "Nostradamus said xyz, pretty weird man!". That was about it, these were just descriptive "isn't it crazy that..." conspiracies. More current ones have deeper implications to their believers, and tend to contain a prescriptive aspect as well.
I think you may be overstating the rise of conspiracy theories throughout the '00s, or rather, understating their weight in previous periods.
If you want to point to the marked rise of conspiracy theorists then you have to at least stretch back to the Kennedy assassination. This is easily the most widespread, actually believed theory, and its impact on people at the time was monumental.
The moon landing theories are obviously prevalent, though likely with fewer true believers and less implications on them.
Even in the 90s this was a rampant thing. Columbine shootings. Cobain's suicide. AIDS.
I would posit that conspiracy theories are a byproduct of mass media. However, you could easily stretch it back further and draw parallels to witch hunts as being attributable to earlier conspiracy theories on a smaller scale.
https://en.wikipedia.org/wiki/Nostradamus_in_popular_culture...