Steven Weinberg says: "Religion is an insult to human dignity. Without it you would have good people doing good things and evil people doing evil things. But for good people to do evil things, that takes religion."
To which Freeman Dyson parried, "And for bad people to do good things–that takes religion."
i) Dyson makes a good point. Good religion prompts some people to do good things they wouldn't do if left to their own devices.
But I'd like to address Weinberg's allegation on its own terms.
ii) There's no such thing as "human dignity" given atheism.
iii) There's a certain paradox in saying good people do evil things. Does Weinberg mean they are still good at the time they commit evil? Or does he mean people who'd otherwise be good become morally warped by religion?
iv) Weinberg thinks his slam against "religion" is devastating, yet there's a sense in which a religious believer might agree with him. That's because Weinberg is attacking religion in general. As an atheist, he thinks all religion is bad. But, of course, religionists are typically more discriminating. For instance, I think Islam inspires "good" people to do evil things. Roman Catholicism inspired "good" people to do evil things. Likewise, the Bible says paganism inspires "good" people to do evil things.
Here I'm using "good" in the sense that false religion can make people morally twisted. Of course, there's another sense in which bad religion is the product of morally twisted people. Those aren't mutually exclusive explanations. Rather, they feed on each other. Bad people invent bad religion, while bad religion makes people worse. They imagine they have an absolute duty to commit evil.
v) Weinberg is arbitrarily selective. Secular ideologies can inspire "good" people to do evil things. Take Communism. A utopian, idealistic ideology that inspired torture, mass murder, &c.
vi) For that matter, some otherwise "good" people do bad things because they find themselves in a coercive situation. Take men conscripted to fight in unjust wars. If they refuse, they will be shot. So they do what's required of them, although they may do the bare minimum.
vii) A final problem is that Christian ethics is incommensurable with secular ethics. Weinberg deems some actions to be evil which Christian ethics deems to be good; Weinberg deems some actions to be good which Christian ethics deems to be evil. There's not much common ground.