Earlier quoted context omitted.
Perfectly rational actors are not strictly necessary. Often it is enough to assume people will act in their own best interest as best they can in aggregate more often than not.
Perfectly rational actors are necessary for the claim that was made. The kind of aggregate best-effort utility maximization you offer is not sufficient for the blanket universal claim made upthread, which requires that every (not the average) voluntary labor exchange is inherently for optimal (not best-effort given the laborers current information) value.
Is it not worth asking why they would choose less for themselves? And, if so, doesn't the act of asking why suggest that we assume there must be an explanation that makes sense? Or do we assume that one out of eight human beings are simply not as rational as the rest of us?
I don't know. I wouldn't let the requirement for perfection completely override the reasonable. The alternative is that there is an underclass of irrational human beings. I think we'd be living in a much different world if that were the case.