alt Hacker NewsThey were definitely extreme by the standards of the time. Their aim was explicitly to completely revolutionise European politics, culture, religion.... everything. One comment I heard recent (on The Rest is History podcast, I think Tom Holland said it) they were the most radical movement in European history.
Their ideology implied at the very least getting rid of whole populations. They wanted to reset to an imagined ancient culture and rewrote history to justify it. Mostly imagined, anyway - Sparta was the one real example they looked to.
They were extreme by the standards of the time, but the Overton window at the time did go further to the extremes, so they were considered less extreme than they would be today.