most of the time, putting ads on a website is just enabling other people to exploit visitor's data, which can also tie in to more direct exploitation and discrimination.
i get the impression that nowadays you're not gonna get more than pocket change anyway without being really active in chasing down google's wild geese.

there is the option of direct relationships with people to put static ads on a site, but i'm not sure if that's a thing outside of sex blogs and related things.