If I were in the position of WhatsApp, I would prefer not to sell user info on principle...but I might also have other principles that say I could do enough goo

If I were in the position of WhatsApp, I would prefer not to sell user info on principle...but I might also have other principles that say I could do enough good in the world with $19B that it overcomes the evil of selling out a messaging app to Facebook. I get where you're coming from, but I think you're ignoring the utilitarian argument that can be made in this kind of situation.