I'm not twisting anything. This is what you wrote: "Slavery can be bad, but slaves could have been able to use the skills learned working on plantations for employment in post-abolition."
You wrote what you wrote, and, like a good rightist, you refuse to even walk back the worst part of it. Just say it: "I know that slavery is bad." By doing so, you're not "giving in to my demands"; you're taking back the part of your soul you amputated when you indicated that slavery isn't always entirely bad. This is about you and your own broken moral compass, not me.
It's sort of funny: you're just walking around in the world, perfectly content with the idea that owning other humans "can be bad." Like, that's a position you're okay with--even more, that you're willing to stake yourself to, despite being given the opportunity to revise. That's you: the guy who, even anonymously, can't write, "Slavery is always bad." Yikes.