Jeremy Stangroom

That depends. If there were good anti-slave arguments in existence, then those who chose to discount those arguments were morally bad. If there were no good arguments, then they could have been simply ignorant.

Hmmmm. Not sure - seems to suggest it is only morally bad to hold slaves if you know it's wrong (not quite what you claimed, but I think that's where your position would lead).

It *is* morally bad to hold slaves, of course, but if a slave-holder has never actually encountered the reasons why it's morally bad, then can he be said to be a bad person?

It seems self-evident to us of course, but maybe it wasn't. Maybe people had to sit down and puzzle out why it was wrong, and it just never occurred to people before that that there might be a problem. They could have just assumed 'it's natural' or whatever.

To say something is morally bad normally entails that a person is culpable for it, but you're arguing they are not culpable... I think that's a tricky position to hold.

Am I morally bad for boiling lobsters today if in 5 years time scientists discover that they are actually in agony, and have a surprisingly advanced reflective consciousness?

No. But not all not knowing is equal. That's the point. Not knowing isn't a sufficient condition for absolution, though it might in certain circumstances - such as your lobster example - be necessary to get you off the hook.

What would be the conditions for absolution?