I’ve alluded before to the excellent wikipedia article on Conspiracy Theory.
This quote from the introduction might be especially appropriate here:

In the United States of the late 20th and early 21st centuries, conspiracy theories have become commonplace in mass media. This has contributed to conspiracism emerging as a cultural phenomenon and the possible replacement of democracy by conspiracy as the dominant paradigm of political action in the public mind. [1] According to anthropologists Todd Sanders and Harry G. West, “evidence suggests that a broad cross section of Americans today…gives credence to at least some conspiracy theories.” (emphasis added)

This means that more and more people see public action as driven by hidden factors like widespread conspiracy, rather than by familiar democratic processes (voter perception, legislative deals etc.).
This strikes me as very dangerous.