What else can Facebook demand that its users use or don't use?
It isn't illegal. Facebook isn't a legislative body or a court, it can neither create nor adjudicate law.
And you can read Facebook's case via their cease and desist letter linked in the article.
> What else can Facebook demand that its users use or don't use?
Outside of their platform? Nothing, obviously. They're not going to break into your house and burn your books or anything.
If it were me, I'd be tempted to martyr myself just to show how fucked up Facebook really is. What is the worst that can happen? The guy goes bankrupt. Life goes on.
They can stop you from developing software for their platform or using their API or brand, which is what Facebook has done. They haven't demanded the developer of Unfollow Everything cease developing software altogether, only that they cease developing software for Facebook.
Also, Facebook is nowhere near unique in having similar terms for developers.
That demand is wrong. What if the developer makes an extension for some other web site and then FB buys that site? They'll go the legal route again. I don't think that is right.