What is "Religion"?
Perhaps you’ve heard people talk about the tension between science or religion or you wonder how science and religion affect one another. Militant Atheists, like Christopher Hitchens, claim that “religion spoils everything.” The problem with this way of talking is that there is no such thing as "religion." There are only religions. We must be clear with our language or it can sound like we're saying something clearly when we're really not.
Defining Terms
Just what is a religion? Belief in a god or gods? Most people consider Buddhism and New Age to be religions, even though they have no gods. A system of moral beliefs? To say that would be to suggest that non-believers have no morals, which doesn’t seem to be true. Belief in supernatural reality? Then you might have to include beliefs in ghosts and zombies and things that many people would not consider religious things.
I believe the most useful definition of a religion is almost synonymous with "worldview": a religion is a set of beliefs about the meaning of the universe (or lack of meaning). Religions make truth claims that usually cannot be scientifically verified, but are defended on philosophical grounds. By this definition, Atheism is a religion, because it makes a truth claim about the supernatural (that it doesn't exist) that cannot be tested or proven; it must be argued from philosophy and ultimately accepted by faith.
Atheists sometimes speak as though science is on their side, but of course science can’t give real answers in the subject of theology; you can't test whether God exists, or design an experiment that could do so. Atheism, like any other religion, must begin in Philosophy 101, and its claim to monopolize science is refuted by observing that the majority of scientists throughout history have held supernatural beliefs, some of them quite strongly (just look up "Catholic scientists" for a sample).
Lumping Religions Together
What these supernatural skeptics often mean by "religion" is the Christian (or specifically Catholic) Church, (which they sometimes lump in with Islam to make it seem terroristic). One problem is that there isn’t a strong philosophical relationship between Christianity and Islam; yes, they're both monotheistic, but the Triune God of Christianity is very different from the Allah of Islam, and humanity's ways of interacting with the two are pretty much opposites. Christians are no more responsible for Islamic terrorism than Atheists are for Dan Brown novels (though I wouldn’t want to be associated with either).
Again, there is no such thing as "religion." There are only religions, and they are each so different that it makes no sense to lump them all together – unless you are trying to make a case for your own religion, but don't want to admit that you too are beholden to philosophy and can't prove your case. Some religions believe in one god, some in many, and some in none. Some hope for the afterlife, some for reincarnation, and some for annihilation. Some expect you to love and serve others, some ask you to make war, and some say that you should look out only for yourself or your own tribe. The religions of the world are very different – except in moral matters, where they tend to agree on the generalities and differ on the specifics.
Since every religion, including Atheism, makes unprovable truth claims about the universe, it seems that the only people who are in a position to complain about all religions are pure Agnostics. But most Agnostics are live-and-let-live people; they're not where most of the vitriol comes from.
Mad at Nothing
Most religions agree that some kind of metaphysical reality exists, even if they disagree about what it is. This means that Atheists are in a very small minority, and it’s interesting to ask why. If you read Christopher Hitchens or Daniel Dawkins, you get the clear impression that Atheists are not so much incredulous about God as mad at Him. I'm not saying these guys represent all Atheists, but they speak for at least some segment of the population. If God doesn't exist, how can anyone be mad at Him? Perhaps they're mad at Him for not existing. The New Atheists will tell you that they're mad about the false idea of God or mad at the people who believe in Him and want to force their beliefs on others.
And yet, some religions are clearly a force for good in the world and a comfort for those who believe. For instance, imagine what the world would be like without Catholic hospitals, Catholic orphanages, Catholic adoption agencies, Catholic soup kitchens, or even Catholic contributions to sciences like genetics (Friar Mendel) and astronomy (Father Lemaitre). Not to mention the personal comfort and sense of meaning that the Roman Church has brought to millions of people for thousands of years. The New Atheists will cry, "But the Inquisition and the Crusades!" But they refuse to weigh any mistakes against the Christian influence in stopping the most terrible and murderous regimes in history, such as the Nazis and Stalinist Russia. I'm not trying to make a case for Catholicism here; I'm not Catholic. I'm just saying that when you're so angry you can't even admit that people you disagree with have done good in the world, then you aren't thinking clearly.
I can admit that Atheists have done some good in the world; for instance, by challenging mandatory religious exercises, which are antithetical to the freedom that orthodox Christianity also champions. We don't want to make anyone believe, either by providing negative consequences or by peer pressure; we believe that the case for Christianity is strong enough that we don't need bullying to spread the Gospel.
Speaking with Clarity
No matter which is your religion, to talk generally about "religion" as an actual concept that has a real meaning is just nonsense. When a word is so vague that using it makes various hearers think of utterly opposite things, that word is not useful. You can't talk about "religion" rationally unless, you mean "every belief system except Agnosticism." But that's not a very helpful definition. So let's be clear with our words.
When you're talking about a religion, use the name of that religion, so everyone has an idea of what you're talking about. And if you really do think that Christianity is the same as Hinduism and Islam and Buddhism and Mormonism, I suggest you learn about what people actually believe and read more widely.
Let's drop all this silly talk about "religion" and let me know if you're talking about my religion. Then we can have a real conversation.