From the Meno:
How could that a mender of old shoes, or patcher up of clothes, who made the shoes or clothes worse than he received them, could not have remained thirty days undetected, and would very soon have starved; whereas during more than forty years, Protagoras was corrupting all Hellas, and sending his disciples from him worse than he received them, and he was never found out. For, if I am not mistaken,-he was about seventy years old at his death, forty of which were spent in the practice of his profession; and during all that time he had a good reputation, which to this day he retains: and not only Protagoras, but many others are well spoken of; some who lived before him, and others who are still living. Now, when you say that they deceived and corrupted the youth, are they to be supposed to have corrupted them consciously or unconsciously? Can those who were deemed by many to be the wisest men of Hellas have been out of their minds?
Made me think of Bill Kristol et alia.