As an economist, I can't say that slavery was a bad thing, slavery brought masses of new products to the shores of Great Britain. I mean, that's if we're talking about the old slavery, getting sugar from Jamaica, spices from India? The money that this produced for both GB and the enslaved countries, is insane. Thinking on the one side, the people within the enslaved countries would be working and creating wealth, while staying alive. While the countries would be benefiting from the infrastructure which GB is putting into the country, allowing them to make their own money in the future. This is a win win situation.
The new products coming into GB would be awesome, they would make the rich people who can afford them feel great, while the empire of GB would be greatly admired throughout the country.
I don't real with moral issues, because obviously, some of the conditions were terrible, but some people would have been dead otherwise. We don't actually know what their living conditions were truly like.
You've got to remember, we're all slaves to capitalism anyway, so what's the difference? Times change and so do norms and values.