Apparently Heinlein wrote the evos *Scripture* because they sure quote it like that. It's pretty pathetic if that's the best they can do. Everybody has some belief system-aka *religion*, even if they deny it.
Whether or not you believe something is irrelevant. Obviously even atheist believe many things. The real question is whether or not you take any belief to be axiomatic. That is the distinction with a difference.
A purely rational person would not assert any axioms, though they may assert that a particular belief is highly probable (c.f. Occam's Razor). I really can't speak for atheists, but I have gathered that most them merely do not take the existence of God as axiomatic. If you have no axioms then you have things like Bayes' theorem and Occam's Razor, which are not a bad foundation for reasoning by any means. The strictest rationalists will fully acknowledge that all of mathematics is based on arbitrary axioms and therefore may be incorrect at its core, but its uncanny effectiveness means that one does not discard it lightly (per Occam's Razor).
You assert that everyone has a belief system, but not all belief systems are equal. Generally speaking, non-axiomatic systems are more rational than axiomatic ones (as a strict consequence of mathematics). The fool takes their beliefs to be axiomatic, a wise person views their beliefs as nothing other than the unauthoritative best answer they have at the moment and subject to change rather than the Correct answer.
I agree.