Slaves were never auctioned off because technically you can't auction off property that is not in proper working condition.
Do you think it is fair to make jokes about black people not working? This is a terrible joke that implies that black people should be slaves.
Yes. We owned slaves for the longest time and we even sold them to other nations. You can't say a thing about it.
The thought that black people are lazy is an age old stereotype and an extreme generalization and is not something right to say. Spreading that idea around hurts black people both emotionally and by the fact that it makes them more difficult to secure jobs in society when they are stereotyped like that. You can help make things better by not joking around that black people are lazy and instead be more supportive of the black people in your life that you encounter.
I think you are reading too much into this.
I'm just saying that you could potentially hurt people, and don't you want to avoid that? Putting down all black people with a single joke doesn't sound very nice.