Clearly the solution is not to try and get it both ways—money for disparaging and money for not disparaging. Most people choose one, not both.

Maybe, but if you couldn't rationalize whatever makes you the most money being ethical then you probably wouldn't take a job at a place like Facebook in the first place.

Conveniently, that makes it easy to write your praise. It doesn't take much to go from "demographics like 'teenage girls with body insecurities' want relevant ads like beauty products! We're helping consumers to satisfy their needs!" to "showing teen girls aspirational images that drive them to buy beauty products (and happen to drive insecurities) is just helping them reach their potential! We're helping consumers to uncover needs they didn't know they had!" Wherever your comfort line was to decide to work there, you can probably drive it a little further with similar reasoning.