Student or Learner
With the expression of "useful", is it that the author thinks that the"descriptions of the universe" are useful? Or "all religions think that the "descriptions of the universe" are useful?
Who Puts the Good in the "Good Book"?
Even if a belief in God had a reliable, positive effect upon human behavior, this would not offer a reason to believe in God. One can believe in God only if one thinks that God actually exists. Even if atheism led straight to moral chaos, this would not suggest that the doctrine of Christianity is true. Islam might be true, in that case. Or all religions might function like placebos. As descriptions of the universe, they could be utterly false but, nevertheless, useful. The evidence suggests, however, that they are both false and dangerous.
The author is saying that religions could be useful as descriptions of the universe. He believes that being false doesn't mean they are useless. But he believes they are neither useful nor true.
"Could be" has to be read in the right way. He doesn't believe religions are useful, but he's saying that it's logically possible.