They are knowingly choosing to let everyone else starve. You might think it is acceptable for them to do that, but at least do so honestly.
According to the rational moral intuitions of those involved. Even Molyneux doesn't go farther than claming that our moral intuitions (at least, the logically consistent and universally applicable ones) can be derived from a set of first principles. Moralist positions such as those presented by Molyneux are essentially descriptivist. The is-ought problem has not been solved, so if you are going to be a moralist you can't really have a rational source for your moral claims other than moral intuitions. Molyneux's view is fine here, and I agree with the principle that the human moral intuitions that are capable of consistent, universal application (categorical imperatives, in the language of Kantianism), but the standards for who can own property according to his views do not really seem consistent with any first principles. My inquiry here can be more succinctly summarized like this: What makes a certain kind of property morally valid, and from what moral principles does such ownership derive?