If the slope is so slippery smooth there has got to be a point in between changing the details of an arbitrarily complex sort and filter default on a social network site and purposely propagating lies.

"Facebook itself could target certain users, whether they be corporate rivals or current/former employees. Having such strong psychological control over your workforce would certainly have its benefits. And if Facebook ever gets caught? Why, the company could claim it’s all part of a social experiment, one that users tacitly agreed to when they signed up.

With over one-tenth of the world’s population signing into Facebook every day, and now with evidence to back the emotional power of the company’s algorithmic manipulation, the possibilities for widespread social engineering are staggering and unlike anything the world has seen. Granted, Facebook’s motives probably are simply to convince people to buy more stuff in order to please advertisers, but the potential uses of that power to impact elections or global trade could be enticing to all sorts of powerful interest groups."

The thing about this case is that network effects of communication services make for very strong path dependence, thus making it extremely hard to get back up the slope a bit if you notice you've been slipping down a bit too much.