Utilitarianism defines utility as whatever people value. The hard part is interpersonal comparisons.

Most arguments I can come up with are reasonably close to contemporary arguments for socialism or basic income. Do you consider those arguments (far more socially acceptable) to be similarly "messed up"?

(Note that most of those who have advocated for slavery in recent years, e.g Obama and Rangell, did so from a socialist perspective. Slaves would serve the state, either as "volunteers" for social programs or in the military. I'm not the only one who finds the cases to be pretty close.)