To make the point more effectively, I wanted to propose one that is a better instantiation.
Consider that you are a refugee in the usual squalid camp. You receive an offer: marriage in a foreign country and all your refugee family members get permanent residency.
Of course the situation itself is the compulsion to slavery, and we should recognize that the general word slavery, in this case refers to one variant, which has some very basic rules and regulations to it – hence it is not the truly unrestricted case. But, this one clearly improves the situation for everyone, including the enslaved, and from a counter value perspective, clearly the sacrifice of the few for the many is an improvement.
Also note that in the unrestricted case (the enslaved arbitrarily can be killed), if the other parts of the contract are enforced (permanent residency/lives/etc.), this deal may still be a macro improvement, in the context of the false dilemma.