One person's extremism is another person's reality. What I believe in is reality, but what you believe in is extremism.
To me, the "bottom line" on this in one word: "relative".
OK, I'll take "subjective" as an alternate.
I gotta stop talking to myself.
I'd have to agree.
I grew up in a Pentecostal-type environment; where my parents still believe in miraculous healing, speaking in tongues, being "slain in the spirit", etc. I certainly consider this extreme. Many do not.
Any belief that exists in spite of evidence or without any evidence, I consider extreme. I find it the true "slippery slope" as the belief in a being that can not be substantiated is already a belief without reason; a belief without evidence. From there, following the pat of believing without reason or evidence or in spite of either or both, those who subscribe to such beliefs are more lucky than anything that they don't fall prey to such evil actions as refusing to permit your children medical care; after all, God will heal them. While this definitely encompasses religion who will believe in an omnipotent being in spite of lack of evidence or in spite of contradicting evidence, it also extends to flat earthers, Sandy Hook conspiracy hoaxsters, anti-vaccination proponents and just about anyone else who will believe a given thing without evidence or in spite of evidence. Anti-vaccine proponents would gladly end vaccination programs bringing, call it good, and wind up bringing back smallpox and polio epidemics; 911 conspiracy theorists would gleefully take down our government, lynching those those irrationally believe were responsible, leaving us in anarchy or with an ineffective government, and call it good; and the religious "extremists" have happily denied their children medical care, beheaded aid workers and those of different religions or ethnicity, fed their children cyanide, murdered abortion doctors, committed mass suicide so the spaceship can pick them up, beat their children to death, burned people alive on a stake, followed Hitler into slaughtering millions of Jews believing "God with us", cutting the hearts out of your fellow citizens to keep the sun from getting stuck in the sky, burying your young under building foundations to ward away evil spirits ...... and every bit of it started, or would start, by believing a thing without evidence or believing a thing in spite of evidence.
It's all cut from the same stone, imho.