Good thread Hugo.
My problem with the Truth movement is that it is very similar to a religious sect.
Anything that would undermine their own version of the "truth" is blatantly disregarded.
But to the actual question. Why do some people, myself included, feel threatened by the conspiracy theorists?
Well Hugo.
Because it's just like back in Germany in the 30's, or when religious mad men tries to take control over education in school.
In all those cases, beliefs would dictate facts.
Hugo, imagine yourself how it would be with a congress filled with people who believe some Jewish family (Rothschilds) is plotting to control the world.
Or a president.

"Mr CIA Director, I want you to investigate the options for how to take care of the Rothschild problem"

Yeah. That would be real brilliant.
Or in the state of the union speech:
"I pledge to the US people that we will get to the bottom of this Illuminati thing. We will go after them at any cost. Anyone protecting them is considered an enemy of the USA"
So yeah. I think conspiracy theorists are potentially dangerous.
They're potentially anti-democratic.
I think you can see the pattern of extremism in these groups, be it right-wing or left-wing.
But I think it's also important to discuss why these types of groups occur.
I believe it is due to a lack of faith in the current political establishment.