Slavery ended in 1865. That's 161 years ago. So maybe there are a few modern 80-year-olds who interacted with 80-year-old former slaves when the modern 80-year-olds were infants. Those 80-year-old former slaves would themselves have no memory of slavery since it would've ended before they could form memories. And the modern 80-year-olds would have no memory of the interaction, since they themselves were infants when the interaction happened.

In other words: There aren't very many of these people, and it's unclear if most of them would count.

You know something which happened more recently in the US than slavery? Prohibition. A trendy, self-righteous moral crusade which didn't accomplish what it set out to achieve, and ended up creating a bunch of problems instead.

I think Prohibition is a pretty good template for understanding the form and tendencies of modern left-wing activist movements. But--at least reducing alcoholism was a good cause that we had a shot at doing something about! Short of inventing a time machine, crusading against slavery from centuries ago seems rather pointless. That's not a problem for activists whose primary goal is to be trendy and self-righteous, of course.