"When the truth is, their adherence to such absurdly costly principles is precisely to signal that, compared to those who cannot afford their morality, they have it easy."

I think the idea that "morality is a form of signalling" is inaccurate. I agree that moral principles have an evolutionary explanation, but I think that standard game theory provides the best explanation. Generally, it's better to cooperate than to defect in the iterated prisoner's dilemma; and the best way to convince others you're a cooperator is to be, truly, madly and deeply, a cooperator.

Cf. Elizier's claim that he wouldn't break a promise, even if the whole of humanity was at stake. It certainly makes him seem more trustworthy, right?