The best response to that I have found is to ask them If priests sleep with young boys only because the bible doesn't forbid it. Then ask if they still agree with basing their morals on religious values.
This is the one that really gets me pissed. I can deal comfortably with Intelligent Design, Irreducible Complexity, Creation Science. But the idea that the only source of morality is the one that Dispensationalist Millenialist evangelical Protestant Christianity decided is the right one just burns me up. And (I actually keep a list in my pocket) when I bring up all of the horrors done from one set of Christians to another, different set, I get told that these people weren't "really Christian." However, all of the items on my list are from times when people were actually true believers. So how many "real Christians are there in the world? Six? Probably not whoever is asking about morals, that's for sure.