None of what you've outlined equates to justifiable slavery. The welfare queen is the only character among your scenarios who has not committed a crime. Therefore, why should she be "enslaved" simply because someone doesn't like the fact that she was deemed (repeatedly) eligible to receive those welfare benefits? All others you've characterized above should do their penance accordingly as the law dictates. Now, if that penance involves making small rocks out of big ones, pressing license plates, harvesting crops on the corporate farm, repaving roads or digging ditches, then so be it. That's part of forfeiting your right to live among a peaceful, law abiding society. But I wouldn't call this slavery. I'd call it imprisonment. No one owns them; they're just locked away from society for the crimes they've committed until time served (less a life sentence or the death penalty).
Now, as a Black man do I believe slavery should never be allowed? I have to say yes. I'm against the ownership of anyone as property. However, I can see where indentured servitude can work because it's no different than being a contract employee only instead of being "hired" to perform a specific task (or tasks), you perform any task assigned to you for the agreed upon timeframe at the agreed upon price. Think Joseph, for example.