In a interview on Closer to Truth he says that science is about questions of fact (I agree) and that it has nothing to say about questions of value or morality. He says that science can explain why people have moral codes but none of that explains why those are things we ought to do. Here is a quote from the interview:
"And in fact, in some cases, what we ought to do, it seems to me, is to go against our biological background. For example, biologically, men and women are very different but I think one of the great things that has happened in the last century is that we've learned that all opportunities that are open to men are open to women also. That we ought to transcend that biological difference where we can. The fact that science has nothing to say about what ought to be but only about what is, has left many people dissatisfied with science [...]. Some people have turned to religion as filling up the rest of what they need. I don't find that satisfactory. It seems to me, in the first place, that historically, religion has not done a very good job of telling us what we ought to do. [...] The message of especially the great Abrahamic religions [...] seems to me fundamentally immoral. Instead of taking as the highest ideal that we should be good and kind and loving to each other, it replaces it with an ideal of obedience and worship of a God who surely doesn't need our support [...] I think the human race has to grow up and give up the search for big truths in human affairs."When one says that science has nothing to say about matters of morality, one might either imply that there is another, more reliable method of acquiring moral truths or that there is no method at all on which to base moral statements. As the end of his quote suggests, Weinberg seems to believe the latter. But if he does not think we can attain truth in moral matters, then what is the status of his 'it-seems-to-me-statements' (that women ought to have the same opportunities as men and that the message of the Abrahamic religions is immoral)? Does he argue for moral relativism? Does he think we should not at all take seriously what he says about women rights and religion because there are no truths regarding morality? Are these suggestions no more valid than the views of a religious fundamentalist who argues that women are inferior to men? if so, where does this leave us?
My question to him is: on the basis of what precisely do you make such 'it-seems-to-me-judgments'? Do you base them on 1) dogma?, 2) intuition?, 3) ‘common sense’?, 4) logic? 5) systematic observation, 6) scientific experiments? Or on what basis should they be made in order for us to take them seriously? For instance, what method should we use to determine whether or not religion has played a good or bad role? By saying we should give up the search for big truths in human affairs and then suggesting some truths in human affairs he is presenting us a paradox, especially because his suggestions sound like big truths.
My view is that any claims about reality (including about values and morals) can either be evaluated dogmatically/intuitively or trough a more systematic and scientific process. This more scientific approach would mean that we clearly define the concepts in our claims, that they are logically consistent, and that there is empirical evidence (see more here).
Morality concerns the distinction between right and wrong or good and bad. In order to determine whether something is moral we need to have a criterion. What this criterion is, is ultimately an extremely difficult question and could and should be a matter of ongoing discussion. But it is bound to be related to the suffering and flourishing of sensing beings. Whenever human behavior has no consequences at all to suffering or flourishing it makes no sense to think of it as bad or good.
Is this complex? Sure. So is acquiring knowledge about health. While we have no definite definition of human health and while it is hard to make definite statements about what is healthy and what not, there is no better way of making progress in this matter than through the scientific approach. I argue that the same is the case for morality. By the systematic observation of consequences of behaviors, practices and systems, scientific methods (systematic, unbiased observation, experiments, etc) can help us gain more insight into what practices help us flourish and which make us suffer.
It won't be easy to discover big truths but the choice is not to either go for big truths or to give up entirely.