I'm not one to normally defend Facebook, but I disagree. Advertising was not prioritized for a huge chunk of Facebook's history, so I'd argue it's not part of their core ethos (it's a necessary evil, if you will). While a lot of their more recent product decisions have been made around revenue generation, I don't think that's what keeps their leadership up at night. Keeping a monopoly on user attention (euphemism is "connecting the world") is their biggest challenge, especially in the ever-evolving social industry.