If you really want to split hairs, I would argue that copying information that is considered secret to it's owner, is stealing in the sense that you are stealing the fact that is is secret from it's owner. It's no longer secret at this point, and you have taken that away from the original owner.

In the context of stealing secret documents from the government - the question is, did the government have a legal right to keep those documents "secret" from its people. Did those documents contain evidence of illegal activities by the government that it was attempting to keep hidden?

Whether or not it's stealing in this case, is irrelevant, imo. If the information being hidden is of detriment to the people and your intent is to share the info with the people it is harming, then I would argue that it's entirely reasonable to share the information.