Come on, all the cool kids are doing it. Lying, that is. Lying is just one more tool to get ahead, but it's a dangerous one. Just like dynamite, it has to be handled carefully or it can go up in smoke. Just ask Célimène. Or Arsinoé. Or, hey, ask anyone navigating the landmine that is The Misanthrope's aristocracy. Little white lies will get you in good favor with the people in power, but have your lies unveiled and it is all downhill for you, buddy.
Molière suggests that lying and deceit are a consequence of civilization. "Natural" man would not need to lie.
In The Misanthrope, lying is merely a tool that is neither moral nor immoral until it is used in either a moral or immoral way.