There are several competing religions, and each claims it has the Truth. We read daily of clashes between Sunnis and Shia. The last time I counted there were 144 different flavours of Christianity. How could they all be true at the same time? How would one determine which, if any, has a corner on truth? I think the most damning criticism of religion comes out of considerations like this one. David Hume pointed this out long ago in his essay on religion. Is there any truth to the claims of religion?
And what about science? Does it do any better? One day coffee is said to be good for you and a week later it is bad for you. Is sunshine good or bad? Is global warming real or just “the sky is falling” fear mongering? Compare religious claims with scientific claims. Religious claims depend on authority. What is different about scientific claims? Don’t they too depend upon authority?
One of the strengths of science is its capacity to resolve controversies by generally accepted procedures and standards. Many scientific questions (especially more technical ones) are not matters of opinion but have a correct answer.
Scientists document their procedures and findings in the peer-reviewed literature in such a way that they can be double-checked and challenged by others. The proper way to challenge results is, of course, also through the peer-reviewed literature, so that the challenge follows the same standards of documentation as did the original finding. [Source]
Also on topic is this discussion between Krauss and Dawkins.