I wonder what "rational rules" you had in mind. In this context it seems you derive those rational rules from science, the science of good and evil. Ofcourse you also state that you are against a science of good and evil, but on the other hand you deny a spiritual domain, and deny faith as the right way to justice. You see when you would admit a spiritual domain, I would be much more trusting that you don't surreptiously have some kind of science of good and evil. But when you talk about rules that are "rational", then it seems to me that you derive the rationality of the rules from the rationality of science.
There are tons of valid scientific arguments for what we should do and what we should not do. For example, "thou shalt not kill", because if you do, you decrease the spread of the species, and bring others and yourself to danger, which will decrease the chance of yours species to survive. Religion is not necessary to explain morality or decisions. It just makes it easier to deal with, which is what religion is all about: hiding from ignorance.