When challenging the ruling that Data was the property of the Federation, Captain Picard had a conversation with Guinan where she talked about 'disposable generations of people' and in response Captain Picard said, "You're talking about slavery... But that's not the issue at all, is it?"
Captain Picard's defense centered around Data's sentience.
Later, Captain Louvois, in her ruling, mentioned that "We've all been dancing around the basic issue, does Data have a soul?"
Was Captain Picard referring to sentience, a soul, or something else when he said, "but that's not the issue at all"?