Religion is an insult to human dignity. With or 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.This comment frequently leads to negative reactions by believers. The problem is that Weinberg did not explain how religion promotes evil.
In general, religion does not encourage evil behavior. On the contrary, religion prides itself on being a source of moral principles. Religious people are not less intelligent or less moral than atheists.
The dangerous quality of religion lies in the fact that it is an unending source of misinformation that causes otherwise good people to commit horrible acts, often for what they consider to be rational reasons. Couple the misinformation with social pressure and encouragement of unquestioning obedience, and you have a recipe for disaster.
Where does the misinformation originate? Typically, it starts with a small number of mentally imbalanced ("visionary") people who confidently proclaim that they have an inside track on the mind of God. For example, Abraham hears voices in his head encouraging him to kill his son, but manages to become the patriarch of the big three monotheistic religions. Similarly, Joseph Smith claims to see angels and hears voices telling him that God wants him to become a polygamist. As William James suggested in Varieties of Religious Experience, founders of religions tend to be on the unstable side.
Why do the masses tend to latch onto the ideas of the borderline insane? A partial answer is that religious leaders are typically charismatic and very confident in their beliefs. Psychological studies have shown that people have an innate need for closure, some people more than others. Those with a high need for closure want all of their questions answered now, and a ceaseless supply of prophets, priests, and gurus are willing to stand up and confidently proclaim the answers.
Add various social psychological phenomena to the mix, such as groupthink, cognitive dissonance, and confirmation bias, and it is easy to see how ridiculous ideas spread. Richard Dawkins refers to these ideas that spread from person to person within a culture as "memes." Memes are the cultural analogues to genes in that they self-replicate, mutate, and respond to selective pressures.
People frequently believe what they are told without engaging in any kind of critical analysis of the ideas or the sources of the ideas, and therein lies the danger. What if a meme tells you that blowing yourself up in a shopping mall is a one-way ticket to paradise? If you really believe in the paradise meme and the martyrdom meme, you would be a fool not to become a suicide bomber.
Sam Harris explained the problem this way:
The most pernicious and uncharitable way of parsing my remarks about Islam is to say that I believe that most (or all) Muslims are evil. The truth is, I don’t necessarily believe that any Muslims are evil—even jihadists. And this is what I find so troubling about the doctrine of Islam. Are most jihadists psychopaths devoid of empathy? I see no reason to think so. If you believe that the creator of the universe wants you to wage jihad against infidels, I think you can be perfectly healthy in psychological terms while becoming a suicide bomber. Secularists who doubt this seem to be the ones devoid of empathy, in fact: They are unwilling or unable to see the world through the eyes of our enemies—even when our enemies tell us, ad nauseam, exactly how they see the world. The most dangerous failing of secularism (and of moderate religion) is that its adherents cannot seem to grasp that some people really believe martyrdom is a path to Paradise.C.S. Lewis observed in Mere Christianity:
But surely the reason we do not execute witches is that we do not believe there are such things. If we did -- if we really thought that there were people going about who had sold themselves to the devil and received supernatural powers from him in return and were using these powers to kill their neighbours or drive them mad or bring bad weather, surely we would all agree that if anyone deserved the death penalty, then these filthy quislings did. There is no difference of moral principle here: the difference is simply about matter of fact. (Emphasis added).Who teaches the "facts" that martyrdom leads to seventy virgins in paradise, or believers "should not suffer a witch to live," or polygamy is necessary for salvation. Religion, of course. These are but a few of the myriad of religious memes sincerely believed at one time or another by intelligent and moral people.
On a more contemporary issue, if you are told that that there is no biological basis for homosexuality and that gay people are aberrant sinners who choose a lifestyle contrary to God's declared word in the Bible, you will not likely be charitable when asked to vote on marriage equality.
Someday, our descendants will wonder how people of the 21st century could be so backward on the issue of gay rights. That doesn't mean we are less moral than our descendants, any more than than the people who executed witches were less moral than we are today. We, and they, are plagued by superstitious "facts" or "memes" that are created and inculcated by religion.
To advance as a society, we must learn that ideas cannot simply be accepted, without question, based on the word of some prophet, priest, or imam. We must learn to apply the teachings of science, which are designed to overcome the tendencies we have human beings to desperately cling to mistaken ideas or be swayed by popular opinion. Only when we turn to science and reason can we escape our dark past and enter the new age of enlightenment.