I do agree that "reason" doesn't give us all our moral values. We takes as a "postulate" (like the Axiom of Choice in mathematics) that human life is sacred -- which can sometimes call for sacrifices from people outside of choice. Should everyone be expected to be able and open to sharing body resources (blood, organs for transplants) to save the lives of others? That is more pertinent today (with medical advances) than maybe it once was, but reason alone won't answer it. Do we all have a moral obligation to future generations, not just the unborn but the as yet unconceived? (Can people who don't yet exist make moral claims on us?) Should everyone stand ready with the skills to raise kids, even they don't have their own? Again, that's a judgment of society. But it does accept the idea there can be obligations as well as rights. Should "non-human" people (like dolphins and whales) have the same rights as us? Would extraterrestrials? Some day we could have to answer questions like that.
The idea of social bonding makes "logical" sense in that no individual's own personal accomplishments, even achieved alone, are meaningful until other people "consume" them. And outcome inequality is inevitable (as it is in nature), so, yes, there has to be some kind of social order, and heeding of leadership.
The author argues away most of the common defenses of gay equality, including immutability and altruism; he also feels it is fine for traditional heterosexual marriage to be privileged (which the unmarried pay for) even when sterile, because it sets the "right" example for youth. In my own DADT book, I had suggested a "compromise": give marriage privileges only when there are actual dependents (pregnancy can count). That is, use results as qualification, not just symbols.
Note: The book should not be confused with Joseph E. Stiglitz, "The Great Divide: Unequal Societies and What We Can Do About Them" (2015), which looks interesting indeed. I'll have to look into this soon.