God forbid. I believe we have already made the choice but we don't always recognize it immediately even though we are acting it out. In my worldview it is grace that guides our morality in the absence of commandments (well, it guides some of us, LOL).
Some of the difficulty with the initial question is the stark difference between individual and group morality. A moral choice that is workable for an individual can be disastrous for a community. So we have to step beyond personal desire. For Christians, this means a degree of submission that is sometimes painful. For atheists, I would think that it would require a continuous reassessment of former choices.
Ultimately, everyone hangs their hat somewhere. Believers look to God, unbelievers look to utility or self interest or atheistic philosophy.
I disagree that atheists necessarily look to utility. I do not consider myself an atheist, but I am sometimes called one, because I do not base my behavior on expectations of reward or punishment.
I have a family for reasons that have nothing to do with religion. I love my family and other people for reasons that have nothing to do with religion.
I look to religion not for motivation, but for the council of thousands of years of experience. Loving and being good are not simple.