An interesting chain of reasoning, but the golden rule is itself a moral decision (you don't have to live by the golden rule – and many don’t) and thus it cannot be used as an a priori premise to get a necessary conclusion. Unfortunately too, even if it could, the slaveholder can still maintain his (or her) belief in the golden rule by asserting exactly what you pointed out -- that a slave is a non-person and doesn’t count -- provided the slave is sufficiently different in race, culture, etc. to be not like the people the slaveholder cares about. You and I think slavery is a very bad thing, but I don’t think you can write an a priori proof of a moral position. If all you want to prove is that slavery is incompatible with a universalized interpretation of the golden rule, then you are saying more-or-less what I have already argued – that slavery is incompatible with the enlightenment concept of equality. That far, we agree!
Interesting turnaround of my logic. It certainly is hard to extricate one's thoughts from one's cultural vantage point. Slavery isn't wrong; I think slavery is wrong.
I don't mean to sound disheartened ;) My point was that even if slavery cannot be proven to be objectively wrong, the only thing that matters for me is that I think it is wrong due to a belief that follows from my assertion that all sentient beings are deserving of dignity, and that slavery is by definition an indignity. If circumstances were to change so that I no longer believed that every sentient being is deserving of dignity, my stance on slavery would follow suit... I don't see that happening anytime soon though.
Not having a sense of dignity=/= not deserving of dignity. A demented and incontinent elderly human is certainly not dignified, but they are certainly deserving of dignity.
No, that was not my intent. Sentient means (according to Merriam-Webster): "responsive to or conscious of sense impressions" Snails are sentient, but I'm not sure how much dignity we can meaningfully bestow on them. My wife makes a living assisting "demented and incontinent elderly human"s -- so I'm not inclined to disagree on that point. I used to use the word "sapient" for what I think you're trying to capture, but that term has problems too. I've enjoyed this exchange, BTW. Thanks!
Likewise! It's been a pleasure exploring this blurry line of ethics, upon which the snail balances :)