I hate the "it was a different time" excuse for these awful human beings. It falls apart if you do any reading from the time. Plenty of people wrote about how shit these people were AT THE TIME. Our morals haven't expanded somehow. Our systems of control have changed to be more sustainable. The ruling class learned that slavery was not sustainable. That's it.
Also, this doesn't give an excuse for the leaders of today. The slave owners of the past are not "less caring" than the current ruling class is. The current ruling class has just better distanced themselves from direct acts of violence while expanding their ability to perform mass violence. Slavery has evolved into mass incarceration for example. We've just normalized our violence into different systems and outsourced a lot of it to the global south.
If you're a Billionaire today you are the equivalent of a slave owner of the past with significantly more violence and control than a slave owner could ever dream of.