In my opinion, I think your pushing a fine line, in terms of language, by dividing the concepts of justification and reason.
I get the point you're making in terms of the individual's moral compass but in terms of fictional thieves, as protagonists, we usually see world building to support the character's choices...and by proxy our judgement of their actions.
In the real world, where we set our actual moral compasses, we don't usually get a supporting narrative of the original owner of an item as a bad/horrible person. So the argument/reasons presented here would resemble self justifications for the act.
But in a fictional setting, we have time to build ...say the Sheriff of Nottingham... as a functioning reason for a thief's actions. The audience has to adjust/suspend their moral compasses to the narrative. That goes to your point on the the reader's decision... but those are only circumstances that can exist in a narrative