All other knowledge is hurtful to him who has not the science of goodness.

[Toute autre science, est dommageable à celuy qui n’a la science de la bonté.]

Michel de Montaigne (1533-1592) French essayist

Essays, Book 1, ch. 24 “Of Pedantry” (1580) [tr. Cotton (1686), rev Hazlitt (1877)]
    (Source)

(Source (French)). Alternate translations:

• "Each other science is prejudciall unto him that hath not the science of goodnesse." [tr. Florio (1603)]
• "All other knowledge is detrimental to him who has not the science of becoming a good man." [tr. Friswell (1868)]
• "All other learning is hurtful to him who has not the knowledge of honesty and goodness." [tr. Rector (1899)]