Religion does: More Harm or More Good?
What's "religion"? What does the classification include and exclude? The distinction between religion and not-religion seems awfully vague at the edges. Is Marxism a religion? (It obviously espouses a Jewish-style apocalyptic eschatology.) Is philosophical idealism a religion? (It's a supernaturalistic doctrine that's often opposed to scientific physicalism.) Is UFO belief a new-religion? (It seems to be the familiar angels and demons, re-dressed in new ostensibly more "scientific" clothing.) Is Freudianism a religion? ...
And how should we go about deciding how much good a religion does? Obviously, if a religion like Christianity or Islam truly offers people salvation and eternal communion with ultimate goodness, being and perfection, then these religions would seem to have infinite value. If we choose not to accept those claims, then we are kind of assuming an atheist view of those religions by default.
Even if we embrace atheism, we still have the problem of quantifying the comfort and happiness that religious faith has provided many people, along with the problem of assessing religion's actual causal role in things that we don't like, like wars and persecutions. While we all have intuitions about that kind of stuff, none of us really has any hard data.
Perhaps the ultimate question to consider in this thread is not so much the positivity or negativity of religious impact today but rather whether any such impact is justified at all anymore. Does religion have any meaning or significance in a world where it apparently is now redundant?
Again, if religion (whatever that word is being used to refer to) is true, then that truth would seem to answer your question.
If religion isn't true (in any of its countless forms, functions and guises) we still have the problem of determining whether it's redundant. What does religion offer people? (I'd guess that different forms of religiosity might be providing many things to different people.) Can we be sure that non-religious alternatives exist for every role that religion plays in people's lives? Can we be certain that these hypothetical secular alternatives are going to be at least as effective, at least as true and at least as desirable? (Naziism might be described as kind of a substitute-religion, but I wouldn't exactly call it truer or more desirable than older and more traditional forms of religiosity.)