This is a really weird question. If it's not prohibited, why shouldn't you be allowed to do something by default? Isn't that a basic thing in all(?) legal systems?
I don't know if this is a rhetorical question or strongly held belief on your part, but this kind of thinking is what has led to such a grotesque invasion of personal privacy via trackers and other data gathering techniques the last few years. Legality is not the right standard. How about basic courtesy and erring on the side of respecting user privacy?
If all of us pushed our behavior to the legal limit, society would likely fall apart. Orderly society only happens because the vast majority of people respect the rights of others.
This is akin to asking who gives Facebook the permission to badly compress pictures? The answer's same.