Why would Lee encourage that? It's a serious question.
The Confederacy was running out of white men to fill the ranks of the Confederate Army. It was a move of sheer desperation.
Lee loathed slavery (and that is a fact) through his own experience with it and he thought it would give the southern cause more sway with England. Queen Victoria and her consort were noted opponents of the peculiar institution although lovers of the southern cotton balls that kept the Liverpool mills spinning millions of pound notes.
My memory may be wrong on this so I’m hoping that others may correct or confirm what I am writing. And please, leave that chore to others, Ms. Dog. I’d hate to see you pawing through that vast liberry of yours.