Some people aren't capable of telling the difference between a fact, an opinion and a lie, and they aren't capable of evaluating evidence. They aren't capable of being sceptical and thinking critically.
They're so arrogant and ignorant that they'll dismiss the opinions of renowned experts, somehow deciding that they know better. It never occurs to these people "actually, maybe I'm full of ****". They just make stuff up as they go along, whatever fits their agenda, and they ignore anyone who tries to interfere.
There are people that voted to leave the EU because "We give 350m/week to the EU". We don't. They could have made this shocking revelation had they bothered to do 5 seconds of research, but they didn't. They don't even know what they want because they don't know what's real and what's made up.
Everyone who disagrees with them is dismissed as having an agenda, and then they decide that they're just as qualified to comment. Scientists around the world said that a Brexit would be bad for the UK, but these Little Englanders knew better.
They're opposed to progress, and actively sabotage it, and they think that anything they don't understand is evil.
These are the people that would have had us keep believing the Earth is flat, and the people that would have kept burning scientists at the stake for their heresy.
And then, when it turns out they made the wrong decision, they just say "well, that's democracy!" and we all have to suffer the consequences.