[Dajjal]

I'm not sure what saint said it (Aquinas maybe), that extremism was a vice that corrupted the virtues of prudence, patience, humility and love!

I think that what you are thinking of is the Aristotelian/Scholastic definition of "vice" as "a deficiency or an excess of a virtue" -- e.g., the virtue of courage is opposed by the vices of cowardice on the one hand, and being rash on the other.

Not exactly the same as a accusing ideological "extremists" of vice.

[eastsider]

Cf. Aristotle, The Nichomachean Ethics.