This is, I think, the basis for Voltaire's criticism of Leibniz: not that optimism denies the reality of human suffering / irrationality, but that it encourages a kind of quietism. If a rational creator or force or system of natural laws has set up inviolable standards of the highest possible good, then it is not necessary for humans to take any action to correct wrongs. Hence the final note of Candide: "We must cultivate our gardens." Without responsibly-minded human action, the "best of all possible worlds" will deteriorate.

One might argue that responsibly minded human action is part of the divine / natural plan, but Pangloss (literally "all tongue") talks about the rightness of the world and never does anything to improve things. He's like the Laputans in "Gulliver's Travels."