Agreed, assuming there is informed consent - meaning the legal owner was aware of what was happening, was intending to provide the data and was not deceived.

Without those conditions, you'd exclude the whole field of social engineering from hacking, which is all about making the owner "voluntarily" copy data to a third party - and is widely regarded a subset of "hacking".

Also pending the specific circumstances under which you "own" data, which may not be identical with owning the storage medium, as discussed in other posts.