I'm not qualified to make a detailed analysis of religion's role in history all in an effort to distill religion to "net positive" or "net negative," and I think _refugee_ makes a good point.

My own personal views of religion could perhaps be summed up in Vonnegut's invention of Bokononism:

Bokononism is based on the concept of foma, which are defined as harmless untruths. A foundation of Bokononism is that the religion, including its texts, is formed entirely of lies; however, one who believes and adheres to these lies will have peace of mind, and perhaps live a good life. The primary tenet of Bokononism is to "Live by the foma that make you brave and kind and healthy and happy."

One of my favorite parts of Bokononism is the description of the creation of man:

In the beginning, God created earth, and he looked upon it in His cosmic loneliness.

And God said, "Let Us make living creatures out of mud, so the mud can see what We have done." And God created every living creature that now moveth, and one was man. Mud as man alone could speak. God leaned close as mud as man sat up, looked around, and spoke. Man blinked. "What is the purpose of all this?" he asked politely.

"Everything must have a purpose?" asked God.

"Certainly," said man.

"Then I leave it to you to think of one for all this," said God. And He went away.

I think that to the degree that religion gives people purpose and meaning, and advocates for people to live in ways that make them brave, kind, healthy and happy, religion is beneficial. Which parts of organized religions really fulfill those aims is quite debatable and subjective.