Religion is a poor source of morality

[RoadRunner79]

Religion is often touted as a good sense of morality.  "If you don't fear god, then you can rape and murder all you want!" some religious people like to say.  Of course this ignores that Atheists aren't killing people in droves, and our jails don't have a disproportionate amount of atheists either.  But that's not the point here.

I think you are misunderstanding the argument.  It is that under naturalism, there is no source for objective morality.  And if there is no objective morality, then you are just appealing to your personal opinion, and lose any argument against the morals of others.

As to your examples from the old testament, I think you need to do some more research.

Rape was okay - Nope
Women who weren't virgins were worthless - Not there

Let's move a bit closer, however.  Slavery.  Not the biblical slavery (which is apparently okay because that was the culture of the time too.  And it wasn't THAT bad!  At least not as bad as modern slavery).  First of all if modern slavery is worse, then modern slavery was developed during a period of Christianity.  Which means that these same 'moral' people developed a system of slavery even worse than the goat herders two thousand years ago did.  The same people that were happy to stone a woman for not being married before having sex.

My understanding is that it was more akin to indentured servitude then what we likely think of when talking slavery.  Also they where released from their bond in the year of jubilee, slaves where not to be kidnapped or sold.  And, it was never said or encouraged to have slaves by scripture.  I'm not encouraging or promoting slavery, but it seems unfair either in ignorance or by design, to ignore that much of what scripture does say about slavery, and the moral treatment of them.

But back to objective morality.  It's not a comparison of behavior nor saying that atheist behave immorally or are less moral (and it doesn't mean that those who call themselves Christians are more moral).   It has to do with the basis for morality.  For the materialist, they have no standard or cause for objective reality, and therefore no reason to be moral other than subjective preference (not that they cannot be).  And if morality is subjective, then it would be a category error to judge someone else by your own standards.