Here is my imperfect attempt to transcribe what I think is the most telling part of the "bad religion" guy's destruction of even the most general of moral principles, as he is, in the atheists' own terms, destroying their materialistic explanations of why that is right.
... There are competing things which are all good like happiness and truth. For example, we sacrifice some happiness when we accept the truth that we're not going to have life after death. Should we tell other people that they're not going to live after they die? It probably will reduce their happiness on the other hand truth has a value of its own how do you balance truth and happiness there isn't any algorithm for balancing that. I think you just have to accept that there is no postulate that allows you to judge how much happiness you're willing to give up for how much truth.
Even people who accept all this will say, all right we're not going to agree on what is the good but at least we can agree on the fundamental principle of morality that something like Rawls original condition [I think he meant "Original Position"] that we should not treat other people worse than we treat ourselves. Rebecca [Goldstein] was saying something like this that everyone equally deserves whatever is good, happiness or whatever it is. That's not the way I feel either. And I think it's probably not the way most of you feel if you think about it because. I could probably increase the total amount of happiness by making my family live on rice and beans and live in a one room apartment and just barely keep enough money to keep us alive and healthy and send all of the rest of the money to poor parts of the world where it would do to me. I'm not going to do that I'm not going to .... and I well, I'm not confessing immorality. I'm saying that my moral feelings tell me I should be loyal to my family.
Similarly when my university tries to recruit a bright young star in physics I suppose I could calculate, well, he could do more good for some other university and the greater good would imply we shouldn't go after him let some other university go after him. I don't care, I care about my university I'm loyal to my university similarly. So there loyalty is a value it's not an absolute value I wouldn't cause, like Edward the Third, I wouldn't cause the hundred years war to advance the interests of my family. But it is one of these things where we have no algorithm for balancing loyalty against distributive justice.
And I think we have to live with that. I think we have to live with the fact that although we can reason and try to uncover what our moral feelings are. And if we get into that I think a very good example would be arguing about abortion ... maybe I'll come back to that in the discussion.
We can reason, the reasoning uncovers how we feel morally and perhaps allows us to identify areas of agreement so we can cooperate with each other and bring about what we want.
I think in the end we have to live with not having a moral philosophy that really works in a decisive way. I think we have to live the unexamined life. I think this is part of the tragedy of the human condition just like we have no absolute way of determining that Mozart is better than Led Zeppelin we feel it but it's not something that we can argue, we can rationally show. We have to live with the fact that... this came up yesterday.... when we discover the fundamental laws of physics from which all in some sense follows, that all other principles follow, we won't know why they're true. This is something that we have to accept, that the position of human beings is tragic and part of the tragedy, that there is no way of deciding moral issues on the basis of - well there is no way of deciding moral postulates which should govern our actions. And in fact we don't have moral postulates that govern our actions when we behave morally.
I'll start by pointing out that it is the moral deficiency of Weinberg's ideology, materialistic atheism, that is at the base of his program of destruction. It is, as Rebecca Goldstein points out later, unrealistic and rather useless in dealing with the problem of how people behave, though I think her natural selection based attempt is totally unsuccessful, as well. It doesn't stand up to Weinberg's attack based on their shared framing. When Weinberg said, "we have to live with not having a moral philosophy that really works in a decisive way," he was, I believe unwittingly, pointing out why we can't possibly live with his intellectual pose in real life, because it will never work to produce moral behavior and prevent the horrible disasters that his preferred framing of familial and professional loyalty bring about, continually.
As in my update in my post the other day, you should compare Weinberg's statements to those of Jesus and think seriously as to which ones would produce the worst of family based plutocracies, oligarchies, crime families, and other aristocracies, corrupt institutions, unequal distribution of goods, material inequality and the political, legal and societal inequalities that are necessary for that. And you should ask which is actually compatible and incompatible with politically effective liberalism.
Weinberg's substitute for morality is far more supportive of the worst of Republican policy than anything Jesus said on the subject*, it is a secularized formulation of what Jesus said which Weinberg is arguing against, using the pose of a lack of absolute postulates for those things he throws his acid on while refusing to do the same with those he favors, physics, even as he grants they also lack the same thing he calls absolute knowledge. His "competing goods" of loyalty, truth, etc. are no more founded in his ideological framing than do unto others as you would have them do unto you.
That universal acid of insisting on the artificial creation of algorithms and postulates such as those in mathematics and physics before you won't tell lies beneficial to yourself or to betray even those closest to you works on those quite nicely. I have not noted that scientists are especially loyal to their spouses and children of first marriages, such as Carl Sagan, though I suspect that if you could do a quantitative analysis, professional self-interest to your university department makes that stand up a bit better.
That Weinberg reassures us that his refusal to accept any kind of moral absolutes wouldn't lead him to start a Hundred-Years-War only shows that he's a conventional senior faculty member at an American university. They are mostly rather a contented lot who don't aspire to make war, except when their meal ticket is threatened. Though, again considering the role that the often asserted atheist-majority of physicists played in producing nuclear, atomic and massively destructive "conventional" armaments during his lifetime, you don't want to rely too heavily on them being uniformly otiose and even mostly harmless. That there is nothing in what's left of his program of destruction of morality to keep a more ambitious, modern day Macbeth in science from killing hundreds of millions is certainly more relevant than his personal lack of desire to do so. Sam Harris, as I'll remind you, has called for that as a rational consideration and in a similar kind of calculation as something that might substitute for "the good", which would last a day and not a hundred years.
A liberal who thinks hard about this won't find anything in materialism to support their liberalism, if their liberalism is a matter of the moral obligation to do justice in the world, real equality, material, social, political and legal, and the preservation and advancement of rights. When someone chooses the ideological position of atheism, materialism, scientism, there isn't even anything that could make the entire destruction of the biosphere and the eventual extinction of human and all other life on the planet an absolute act of immorality if an atheist, so able, choose temporary self-interest over the continuation of life, itself. You need to exit the framework that is materialist atheism to assert why they shouldn't.
* For example, from Matthew, the continual insistence of Jesus that you had a moral obligation to act morally outside of your family and inner circle, that even the gentiles and tax collectors and such were nice to their family and friends. The elite 1% are the relevant modern day equivalent. Weinberg is saying there is no reason for people such as those at Carroll's discussion group to act any better than they do and he, from an atheist, materialist and scientistic viewpoint, successfully destroys all of their attempts to make natural selection come up with a reason for him to not do just what he wants to. And he's considered something of an expert on such things among pop atheists, frequently presented as such, one who is constantly being thrown in other peoples' faces on these issues.