You can't get to a better future by demanding that it have existed in the past.

That doesn't make any sense.

Now I'd really like to hear these 'good reasons' and what makes them 'good'. Before you list them, please try and apply them to 'why should we abandon slavery'. If your arguments work for both instances, please explain why we ever abandoned slavery, since clearly there are 'good reasons' for owning slaves, so much so that Americans fought a civil war over it last I checked.