A learned fool is more foolish than an ignorant one.
[Un sot savant est sot plus qu’un sot ignorant.]
Molière (1622-1673) French playwright, actor [stage name for Jean-Baptiste Poquelin] The Learned Ladies [Les Femmes Savantes], Act 4, sc. 3, l. 1296 [Clitandre] (1672)
(Source)
Alt. trans.:
"The learned fool is a far greater fool than the fool of ignorance." [tr. Wormeley (1895), The Female Pedants]
"A learned fool is more foolish than an ignorant one." [tr. Van Laun, The Learned Ladies]
"A learned fool is more of a fool than an ignorant one." [tr. Wall (1879), The Learned Women]