Since it comes from the Latin word for "root," why do we refer to those who go out on a limb as radicals?
Oh, Geoff--only you would think that up!
But I have to say that I agree that there has been a shift.
I didn't know that it first simply meant a thorough change (thanks, tsuwm). Nowadays if I hear someone called a radical, I invariably perceive a connotation of "crackpot" or something similar.