I think everyone should wear makeup, for four reasons.
Reason 1: Makeup lifts your mood. The London College of Fashion did a study of over 1000 women; 85 percent of them said they felt better about themselves and more self-confident when they wore makeup.
Reason 2: According to the same study, most women expect their female co-workers to wear makeup. Also, I have found through working in retail that female customers expect the women who wait on them to wear makeup. (At one store I worked at, we had three customer service desk associates. One wore no makeup. One wore a moderate amount and the third wore quite a bit. We had a lot of non-regular customers; they would go first to the heavily made-up clerk, then to the lightly made-up clerk and finally, when they got tired of waiting in line, to the clerk with no makeup. One day the three of us made up the fresh-faced associate, and she started getting lots of customers.)
Reason 3: Everyone needs some time to themselves every day. Unfortunately, demands of family and employer can keep you from getting any. If you wear makeup, you can use "mommy's putting her makeup on, and she'll be with you when she's done" as a near-perfect way to keep from being harassed for a few minutes.
And reason 4: It is fun to play with.