Of course, in addressing the issue in general, there are certain assumptions that must be answered in and of themselves before any significant response can be made, namely the issue of atheism itself.
It would be fair to point out that, as a worldview, atheism has many assumptions that cannot be based in and of itself. It takes matters of the question of morality and logic, which are inherently linked to one another, for granted without giving substantive thought to the questions raised by the assumption. Listen to any number of debates on the issues that have been done, by Christian apologists against atheists (such as this one), and the question immediately becomes clear. The atheist will charge, “X is evil”, to which the prudent apologist will, and should, reply, “How do you in an atheistic and/or materialistic mindset come to that conclusion?” Of course the immediate reply is most often about “consensus” or “pain” or “flourishing“, but then again they raise more questions than answers to the question raised by the apologist. Apart from stealing from the worldview of a theist, there is no absolutely certain means of saying that a behavior is “right” or “wrong”, and a atheist, because he or she has locked into the presupposition that there is no God, cannot see the inconsistency of their worldview.
Of course, the retort is that, “Well, I don’t get my morality from a 2000 year old book.” But that’s not a response either; at best it could be a straw man, at worst a non sequitur because it seems to assert that foundations for morality couldn’t be written down or discussed in a rhetorical form, no matter the age of the work in question. Ultimately it is the unfounded assertions that must be dealt with, and dealt with decisively.