In my latest podcast (MP3), I read my Globe and Mail column, Why do people believe the Earth is flat?, which connects the rise of conspiratorial thinking to the rise in actual conspiracies, in which increasingly concentrated industries are able to come up with collective lobbying positions that result in everything from crashing 737s to toxic baby-bottle liners to the opioid epidemic.
From climate denial to anti-vax to a resurgent eugenics movement, we are in a golden age of terrible conspiratorial thinking, with real consequences for our species' continued survival on our (decidedly round) planet.
Ideas spread because of some mix of ideology and material circumstances. Either ideas are convincingly argued and/or they are delivered to people whose circumstances make them susceptible to those ideas.
Conspiracies aren't on the rise because the arguments for them got better. The arguments for "alternative medicine" or against accepted climate science are no better than those that have lurked in the fringes for generations. Look up the 19th-century skeptics who decried the smallpox vaccine and you'll find that anti-vax arguments have progressed very little in more than a century.