Full Idea
The Stoics say that folly alone is evil.
Gist of Idea
Stoics say that folly alone is evil
Source
report of Stoic school (fragments/reports [c.200 BCE]) by Sextus Empiricus - Against the Ethicists (one book) II.90
Book Reference
Sextus Empiricus: 'Against the Physicists/Against the Ethicists', ed/tr. Bury,R.G. [Harvard Loeb 1997], p.429
A Reaction
This is Socrates' intellectualist view of weakness of will. Is the evil in the succumbing to a temptation, or in the intellectual error that leads to it? 'Folly' in English is stupid action, not just stupid belief.