> If Spotify and Netflix are legally obligated to not store any data they do not need, then Facebook can actually make an additional argument that it is ok to give them wider access; after all, the law will ensure they have to handle it properly.

That seems like a huge perverse incentive. Companies will start constructing systems so that more data is "required" so they can legally collect and share more of it. Then convincing them to collect less would require not just convincing them not to collect the data but convincing them to undergo the expense of redesigning all their systems to not "require" it anymore.