I know some overly-assertive atheists who make statements about "religion" as if anything at all spiritual is stupid. To say I don't want to discuss religion is a bit different. Any suggestions?

A debate is when people get together to talk with and listen to each other, to get feedback and to be ready to change their minds if the other has convincing arguments. At the very least, each party should come away with a broader insight, even if they stick to their own ideas. What you describe is not a debate, as they are not ready to discuss anything, so why waste time on them? Religion is not the same as spirituality; atheists can be spiritual, and any atheist should march along in protest whenever freedom of religion is in danger, let alone if they themselves are the cause of that danger.