Though the altruistic approach seems good on the surface, even to theists, especially Christians, upon further reflection on how this value actually plays out in the real world, one can see the cracks in the secular altruist's argument. Mainly, how do we define what is good for all of society? We as individuals, cannot determine what is best for society, for we can never have a complete enough picture of what society most needs, at least not to a moral certainty. Moreover, is the simple fact that no individual can act on behalf of society.
Altruism seems good, even Biblical, but cannot serve as a code of ethics. The problem with altruism isn't that self-sacrifice is bad, it's that it allows society, not the individual, to make the call on who is required to sacrifice their own best interests and why. Society is the majority, and altruism makes one's actions subject to the need of the collective.
We've all heard someone ask: “Who are you to judge me?” or some variant of that question. It's a defensive question usually asked by someone who reasonably expects to be judges harshly by their peers for some ethical or moral transgression. It's safe to say that someone secure in the notion that society or their peers would judge their actions favorably, is not going to pose this rhetorical question. A good retort to that question might be: “Who are you that you are above judgment?”
When we base rights on what is good for society, that begs the question: Who speaks for society? Throughout history, such people who claim to speak for society inevitably turn out to be tyrants. You have a few, even a single person, deciding what is good for the people. Rand thought that people ought to decide for themselves, based upon rational self-interest.