To answer this question, one will have to do some research into Molière, his career as a playwright, his career as an actor, and the significance of his mustache. Before taking on the role of Alceste in The Misanthrope, Molière played explicitly comedic roles. Once he figured out how to perform without a mask, Molière grew a mustache and a goatee to highlight his humorous facial expressions. In a sense, Molière marked his foray into a less funny, more serious role by getting rid of his mustache. It’s similar to how performers right now might change something about their appearance in order to signify a new stage in their career.
While it’d be wrong to identify The Misanthrope as a drama proper (there are many funny moments), it did not, in the minds of a fair amount of audience members and critics, contain the same level of farcical merriment as his previous plays, including 1662’s The School for Wives and 1664’s Tartuffe.
Alceste’s severe scorn for hollow society can be construed as over the top. Yet Alceste is not devoid of complexity or emotion. Despite his desire to "flee all humankind," he still has feelings, particularly for Célimène. The significant strand of sincerity and depth in The Misanthrope separates it from Molière’s past plays, which, again, is signaled in Molière’s choice to move on from his popular mustache.