a) the network effects that make people join the network even if they wouldn't want to on their own
b) Facebook's own agressive strategies of bringing users into their network without conscious choice - e.g. the acquisition of whatsapp or the internet.org initiative.
At this point it's more like some property shark who'd buy up half the city's apartment blocks, then proceed to cut services and raise the rents - and when people complain, respond "well, for some reason all those people chose to rent my apartments, so they must approve of what I do"...
> But until people are willing to get upset enough about issues like this to leave Facebook, they really have no incentive to change.
They will have an incentive to change if e.g. advertisers start worrying about their image if they advertise on Facebook too. Causing outrage and creating a debate around whether Facebook is damaging our society is a way of making Facebook a less attractive advertising channel as well.
Removing that picture for being pornographic should be much more controversial than the controversial pornographic aspect. The latter is really an US-centric notion.
I fully agree with people taking note and becoming aware that Facebook is simply a business providing them a service and not a benevolent social network uniting the world.
But until people are willing to get upset enough about issues like this to leave Facebook, they really have no incentive to change. It's a reflection on society more than on one company. Like it or not, we use Facebook because we like it, it provides a service we're happy to consume. If we're happy and the advertisers are happy why would they care about these sorts of things?