The truth is that slavery means owning another human being, wholly and completely, and so represents an unqualified abhorrence. Whether you need to beat them to maintain that reality- and let's be very clear, the amount of violence deployed in these relationships is at its root matter of necessity, not sentimental disposition- is a fact so irrelevant to this judgement that introducing it could only be suspicious. We may as well point out that the inmates of the Nazi death camps were provided with latrines rather than having to crap in the corner, because, hey, it's just facts, right?