It seems like it would depend on the details. In your example, I might agree that there is net harm to the world. But in other cases, and maybe Jeff's, the harm done by working on ads may be more than offset by the lives saved.

Since Jeff is a thoughtful guy and this is important to him, I'm inclined to think that he is producing net good. If you can convince him otherwise, he'd probably change what he's doing.

At best his work is annoying to a lot of peoole. At worst, he profits (a great deal, I might add) from a industry that exploits, manipulates, and coerces.

It's not really my or anyone elses job to convince him.