[bpodgursky]

Nobody in an extremist group thinks that they are an extremist. To them, it is the obvious rational and right mindset.

You may be in groups (or hold opinions) that others out there consider extremist, but to you feel very natural in the circles you associate with.

[zarzavat]

This is it. Take abortion, one side thinks that it is extreme to kill what they perceive as children, and the other side thinks that it is extreme to limit women’s rights to what they perceive as a medical procedure.

When you get to the bottom of these things you find different axiomatic beliefs. Some of these axiomatic beliefs are not based in truth but that is not relevant to the people who hold them.

There’s also a kind of tidal motion insofar as some beliefs move from the fringes to the mainstream (e.g. lgbt rights) and other beliefs move from the mainstream to the fringes. There’s always going to be some people who disagree with that motion, indeed many elderly people hold “extreme” beliefs (overt racism, etc) they are just not politically active usually.