Suppose I want a slave, so I decide to clone someone and make the clone a slave. Since I'm feeling charitable, I'll let the clone go free after 30 years. I have no interest in making the clone if they can't/won't be my slave.
Most people would agree that this would be morally wrong, since people shouldn't be slaves and all that. But wouldn't the clone likely prefer slavery to non-existence? If we could somehow ask the clone (who didn't exist yet, so it's really impossible, but we can probably confidently predict what his answer would be) whether I should go through with my plan, wouldn't he probably say "Yes, by all means create me, even if I'll have to be your slave for 30 years!"
I think it's interesting that most people would agree that I shouldn't clone myself a slave because it would violate the rights of the clone, even though the clone -if he existed yet- would almost certainly beg to be created, preferring 30 years of slavery to nonexistence.