What about extremists of love, hmm? They just love humanity so geddan much that they give all their stuff away and serve the poor for the rest of their lives through corporeal works of mercy?
That's extremism right there.
C'mon, man, you can't just throw out these words and expect to cover every case, or shut down any argument just because they're 'extreme'!
I mean, if there is a right and wrong, there's got to be some political order or religious order which is correct, or most correct, is it then wrong to be passionate about the truth, and seek to better humanity through it?
Sure, there are plenty of people who are extremely evil, but the degree is not a classification or group that it makes any sense to blame.
Would you rather we all were complacent? What if I said that those who were not extreme in their convictions would simply be slothful and idle all their lives? How are we expected to progress in technology or the material wealth of society?
Heck, Albert Einstein, quoted in your signature, had an incredibly powerful conviction, namely that the universe was an ordered place, and he decried quantum mechanics to his death, attempting to prove in his life that there was some way to know the world outside of it. His dedication was extreme, and admirable.