Socrates agrees: "no one ever knowingly does wrong". :) And a nice essay on the subject: https://midnightmediamusings.wordpress.com/2014/06/24/socrat...
As a PM, though not one that works at Facebook, I would probably approach it something like, how do we ensure that our users stay interested in the homepage, coming back as often as possible and staying on it as long as possible?
There are lots of other sites competing for attention, and to sacrifice a good UX would be shortsighted, especially with all the “FB is dead” comments people have been making the last few years.
And, to be sure, many will justify it by saying "by maximizing this revenue, we're able to provide even more services that people love for free." Is it a Faustian bargain if practically everyone is begging to be Faust?
No one would directly attempt to be evil, it'd just turn out that way.
“The truly terrible thing is that everybody has their reasons.” ― Jean Renoir