Conspiracy theorists have been called many things throughout the years, but one of the things that they have commonly been called (and to many skeptics, accurately called) Fascists.
Now one of the things that made me start think about this claim is a question that I thought to myself "why do so many skeptics tend to call conspiracy theorists 'Fascists' when so many conspiracy theorists claim to opposes Fascism to begin with?" In fact many conspiracy theorists claim to support Libertarianism (or at least something that isn't anything like Fascism), rather than Fascism.
Finally after going to multiple conspiracy theorist websites and reviewing the comments left on those websites, and articles on those websites themselves I have finally come to the conclusion as to why conspiracy theorists are accused of having a Fascist mentality: They have a "Us vs. Them" way of thinking, and they believe that only they are correct.
Conspiracy theorists will claim that they want their "theories" to be given equal consideration and be on equal levels with what is official, but from what I have observed with their behaviors, that isn't true. They don't want their theories to be given equal ground, they want their theories to be considered "fact" (even after the fact that their claims have been discredited and dis-proven), and what is official and actually proven to be true to be seen as a big lie, because in their minds it is a big lie, and they don't want others to think otherwise. In fact it very seriously angers them when someone questions their "theories" (hypothesis would be a more accurate word) or has tested their "theories" and have proven them to be false.
Not only do conspiracy theorists tell other conspiracy theorists (and those curious about conspiracy theories) not to trust the information from reliable sources, they will insult you, question your intelligence, call you a "sheep" (at the very least), and basically try to use intimidation tactics to try to force you over to their side, if you question their "information".
Another thing that many conspiracy theorists will do is that (if the have the ability to do so) they will remove comments that offend them on websites when they can. In fact one famous Youtube vlogger and conspiracy theorist by the name of Christopher Hudson is notorious for this, often times blocking any comments that are in any way critical of his videos. Of course he isn't the only one either, but one example of many people on Youtube, or Facebook, or any individual blogs that promote conspiracy theories and don't allow people to question them.
Sometimes this goes even further then that by not only dis-allowing criticism on their own turf, but sometimes trying to get any criticism of their beliefs removed the internet entirely. They do this either through the use of threats and harassment, to actually trying to have a website shut down.
These are just few of examples of many of the actions and thinking that many conspiracy theorists tend to have and do, but there are many more than just what has been stated.
The reality is that these conspiracy theorists have, as a result of their self-delusions and frustrations over not being able to get the positive attention that they believe their "theories" deserve, they have basically become what they are claiming to fight.