Something you can only believe, is faith. If faith unites people into a community, it's called religion.
And ideas, regardless of their content they have, are the basis for any kind of faith.
I'm just an atheist, but I think, as atheism is sometimes lived, that's nothing more than religion. The fundamental somebody defends his ideas, the more intense is his faith. So here an idea elevates to faith. And in a community it is religion.
e.g. if you don't see the principle, you can't say that Buddhism is a religion. Although Buddhism is very transcendent and stuff, it is a religion that originally knows no deity.
Buddha isn't God or any kind of it.
But we shouldn't go around in circles. Perhaps we can agree, that what I call religion, e.g. atheism, works under certain conditions similar to a religion, according to your definition of religion.
"Life is that prison you'll never leave alive."