(Analogues may be found at the political level, e.g. imposing democracy on a country where the majority don't want it. Of course, Rousseau intended the quoted phrase rather differently, but never mind that...)
But what's a liberal to do? Faced with an informed and considered request for paternalism, you're damned if you do, and damned if you don't. But which level of paternalism is worse? This question may serve to clarify the value we see in autonomy. If we see autonomy as an objective value, then we may embrace meta-paternalism in our quest to see this good realized in the world. (Similarly for the imposition of liberal values on intolerant cultures.) This is a perfectly consistent position for liberal objectivists, and I have some sympathy.
Those more inclined towards the humility of relativism would refrain from ascribing any objectivity to the value of autonomy, and instead seek to respect others' ultimate values. If one of those ultimate values is servitude, then it seems like the humble thing to do is boss them around as they wish. (Democracy unpopular? Well then, the people have spoken. Who are we to deprive them of tyranny?) The most thorough anti-paternalist would accept mastery of the willing slave, accommodating their chosen lifestyle by
Meta-paternalism is the deeper form of paternalism, violating the more central preferences of the person. Still, you might find it intuitively less objectionable. We think that people shouldn't be allowed to sell themselves into slavery, no matter how deeply they desire it. There could be utilitarian reasons in play here, but I will set this possibility aside for now. The alternative explanation is that we are really objectivists about value, and consider the autonomous life to be that which is most worth living -- no matter what the person actually living it has to say on the matter!
(As a welfare subjectivist but moral objectivist, my view is a bit more complicated, and requires treating the individual and societal cases differently. Each individual is the ultimate authority on their own wellbeing, but they're stuck with moral obligations to others whether they like it or not. Hence, I think we should respect people's ultimate values insofar as they don't harm anyone else. If you want to be my slave, go for it! But if you value pushing other people around, even if they form a sub-class of "your culture", then -- as with domestic violence -- I think we have to step in and lock you up. You may sell yourself into slavery, but not your sister. That's where cultural relativists go horribly, horribly wrong.)
(Actually, I think there are pragmatic reasons for disallowing even voluntary slavery, but I'll discuss that in a future post. This one is more concerned with the question of principle.)