All the way back in 2010, myself and @JamieJBartlett studied the effects of believing conspiracy theories. The original report caused all kinds of rigamarole I don't wish to be repeated, but I do think a few points from it are worth re-stating. [thread]

https://demosuk.wpengine.com/files/Conspiracy_theories_paper.pdf?1282913891

1) Conspiracy theories cause a series of social effects beyond simply the belief itself. They allow small groups to form and seal themselves away from 'compromised mainstream discussions and evidence.

2) They silence dissenting voices because they're written of as agents of the conspiracy. An irony is that whilst they're often posed as questioning of the official account, you see individuals mounting internal challenge getting swarmed, doxxed, outed.

3) Yes, they can be spurs to action, even violence, because in their eyes the conspiracy has compromised the other legal/social/political opportunities they have for redress. If the judges are in on it, you're obviously not going to get any joy from the courts are you?

4) When this first came out, many people thought we were saying that all conspiracy theorists were terrorists; which is of course nonsense. There are plenty of entirely non-violent, peaceful proponents and groups who are fully committed to conspiracy theorising.

5) finally it's worth pointing that of course conspiracies exist and of course healthy democratic societies require skeptical citizens. Drawing the line between skepticism and conspiracy theorism is definitely murky, but tends to come back to simply where the evidence guides you