Considering vast crowds of folks happily working for amoral places like investment banks (2008 crisis and its consequences) or wealth management (rich folks trying to keep as much money untaxed as possible and used for public spending), the moral bar for usual smart person is actually pretty low. Optimizing some ads seems pretty harmless when compared to.

As long as you don't see the evil being literally done ie in form or row of inmates being sent to gas chambers, there are almost endless ways to persuade yourself that all is actually OK and fine.