I think we're essentially in agreement that an act can be wrong without being "sinful."  That kind of act is in a category that Thomists call "objective sin" or "material sin," as opposed to "active sin."  You don;t like the semantics, and I understand that, because "sin" in modern understanding entail the subjective --- knowledge and intent.  But Augustine and Thomas knew that very, very well.   They just used the word "objective" in a sense that leads to confusion, and that's where you get confused --- with the word "objective."  While it is true that "sin," as we moderns now understand the word, requires "subjective" elements (knowledge and intent), it is a mistake to say that these subjective elements entail the conclusion that there is no objectively sinful act.  For if you say that, you say there was nothing objectively sinful about gassing 6 million Jews, or bringing Africans here by the millions in slave ships, or raping children in war, or assassinating Lincoln.