The "sharing" of contacts lists is surely the original sin of privacy on the internet.
It's an absolutely outrageous proposition when you think about it. "Give us the names and numbers of everyone you know, whether they consent or not." By triangulating this particular data, the tech giants (and even some of the more successful app developers) know more about us than our governments do.
It's infuriating that this practice has been accepted as normal. It makes it almost impossible for individuals to choose privacy, i.e. without being grassed on by their oblivious friends. It should never have been allowed.