Basic horseshoe theory. It's mostly correct you get hardcore extremists that know they are absolutely right and that any sort of discussion or debate is bad because why would you even let yourself get fooled by some evil person that wants to corrupt your own pure perfect thoughts. Gotta force everyone to be the same as you.

Very different than being opinionated and open to debate. I might think I'm absolutely right about certain things and other people are totally wrong, but generally happy to discuss things with most reasonable people because I don't think they are wrong because they are evil, just because they are ignorant. If they know the same things l know they'll agree with me. Of course the opposite of that also plays true, if you consider your ideological opponents to not be evil, or idiots, but working off of wrong assumptions and incomplete information, you also must be curious to their own reasoning, which requires you to understand what they actually think, and that opens you up to ideas and information you might not have considered,

Ultimately that tends to lead people from the fringes to what we'd consider more centrist ideas. I think a lot of it comes down to context as well. I've had a lot of really stupid arguments with people that boil down to essentially, I agree with your idea in limited contexts buy don't think it is applicable to the average situation.

Mass transit development for example. High speed trains are excellent, so we should build them everywhere. Is an argument I see often. The counter extreme is "public transportation sucks, we shouldn't waste money on it".

My position is more "high speed trains are excellent, in high density population corridors, and suck everywhere else" which tends to piss off everyone on both sides of the issue.