What makes your brain function, e.g., make the decision to eat a peach instead of a strawberry, or rob a bank instead of getting a job?
This would purely be based on aspects involving past experience, individual judgments of pleasure, and a bit of chance.
I decide, and YOU decide. Do you think the decisions of men (and animals, if you choose to include them in your deliberations) are completely and totally material/corporeal/comprised of matter (however you want to say/understand it) and involve nothing apart from “matter?”
Almost always a matter of balancing priorities. One weighs the benefits against the drawbacks, mentally. Not merely physical or tangible ones, but also the intangible. One weighs short-term gains vs. long-term consequences. This is why morality becomes flexible, in a way, depending on circumstances, and not robotic or rigid:
WATCH: http://www.ted.com/talks/dan_ariely_on_our_buggy_moral_code.html
So to summarize your thrust, all you believe exists is a physical universe with NO immaterial beings (spirits).
Correct?