So their economic platforms are the same? Because that's what left and right refer to. Like, if you said the same thing for the authoritarian/libertarian axis of the political spectrum you'd sound insane. I'm not denying that people on the left and right might share some bad opinions, but it's politically illiterate to say that it's because they're so far left and right. The far left is for the system to be able to support everyone. The far right is for the system to allow certain people to get ahead in such a way that it can completely fuck over someone else because "they didn't try hard enough". They could not be more diametrically opposed.
I would actually say that because they're so far away from the norm is the reason they have those questionable beliefs.
Two main reasons that I can think of
1. It's more likely for irrational people to fight for a cause that isn't doing well. Not to say they're a majority or anything just that they're less likely to be turned off by failure and such
2. Being as extremely opposed to the norm attracts people who have views that exist just to be contrarian. This leads to some beliefs to be exaggerated and the general distrust of the people currently in charge and a decent bit of conspiracy theories
I don't think this line of thinking is endemic to either end of the spectrum and that if either would have been the norm those types of beliefs wouldn't be part of their ideology.
But for actually becoming the norm, I can't see the right being able to divorce themselves from such things but I'd definitely expect the left to be able to shed most of it
