Crude on whether atheists are as moral as theists

Here. 

One 'trick' I'm particularly tired of is this: "Atheists are just as moral as theists, so you theists better say this if you want any dialogue with atheists." Except A) Who wants dialogue with atheists, particularly New Atheists who are bound by politics more than anything? And B) On what grounds do I say atheists are as moral as theists? My stock reply is, oh, so atheists are typically against abortion, gay marriage, premarital sex, and other things I view as immoral? And that usually seems to shut down that move, if only for that particular moment. 

This raises an interesting issue-when you compare atheists and theists morally, how can this be done when the parties don't agree on what morality amounts to.