Sometimes one will hear theists claim that religion is necessary because it buttresses morality or produces more moral people. When they do so, they implicitly concede several points.
The first implicit conception is that theists and non-theists both find morality (however defined) worthy of protection. After all, why ask non-theists to protect morality if they have no morality? This grossly undercuts the favorite ad hominem claim of our intellectual opponents, namely, that only religious people care about morality, that non-religious people don't and therefore non-theists' points need be given no attention.
The second somewhat related point is that morality is capable of being measured without reference to religious claims. If all that, say, a Christian has against murder is that the Christian Bible prohibits it, then murder's un-Christian character is tautological. But if one must first accept Christianity to reject murder, then rejecting murder is at most a result of Christianity, not an argument in favor of it any (unless one indulges the sort of special pleading that Christian morality, like Mom's Christmas cookies, is the sweetest.) Morality thus boils down to equivalent of the private prejudice that my sweetheart is handsome/beautiful and my children brilliant, because they are MINE - inflicting thus catastrophic damage on Christian moral claims.
Either morality has meaning, valence, outside of Christian definition (thus raising the value of Christianity as a means thereto) or morality outside of Christianity has no meaning, in which case Christianity's morality is no greater significance that the fame of some celebrities have for being, well, famous.
If on the other hand right and wrong exist outside of Christianity (or any other religion with supernatural claims), and Christianity can be praised for upholding the morality the best, what is the content of that morality and whence comes it to us? If Christianity is merely a useful guide for living a good life (again, good defined outside of its own internal sphere), why is it better than Aesop's fables or the rules of procedure for traffic court before the nearest town magistrate or its equivalent, or for that matter the NFL rulebook?
Christianity (and other religions) cannot bootstrap themselves as moral guides without answering, or at least addressing, what is objectively good and why in manner rationally persuasive to the non-Christian. Otherwise, accepting the moral claims of Christianity as a Christian under Christian jurisdiction is no different from agreeing that when you pass through Yardville's jurisdiction you will keep your speed down to 25 miles per hour as a Yardville motorist, or that a neutral zone infraction carries a 5 yard penalty within the NFL's jurisdiction. If you aren't a Christian, a Yardville motorist or an NFL player or fan, you are simply outside the jurisdiction of the Christian worldview, Yardville traffic code or NFL rulebook, and cannot logically expect to give those sets of governing principles or rule meaning in your life. Conversely, if Christian morality is more than an in-house code for Christian worshippers and has moral merit as an asset, that asset must be measurable outside the Christian rulebook itself.
Either way, when Christians "sell" Christianity as a moral bulwark, they concede that Christianity itself is not the source of the claimed value it seeks to protect; otherwise it's not persuasive or valuable to any outsider, at least on that basis. Same with any other religions' alleged "moral utility."