I am sorry, but that simply is not true. Back in my undergraduate days, studying anthropology, I learned that belief in a single deity is not at all universal. In fact, the belief in deities is not universal. The only universal belief or practice among humans is that all human cultures practice some form of marriage.

It also seems to me the fundamental issue is separation of church and state, a constitutional issue, and your point is somewhat irrelevant. It is also unconstitutional to ignore the atheists, and agnostics, even if you happen to disagree with them