The point, of course, that we are getting away from is that due to it being that old, the 'the bible says it's OK argument is just moronic'.
While at the same time the 'yeah but the Bible says slavery is OK' argument is just as flawed because they both ignore the fact that the Bible doesn't really have any authority today because we live in an utterly different world than we did then, but also that things being in the Bible which we don't agree with cannot be used to attack Christians because they were typically things which were accepted by all cultures and religions of the period.
It's funny also to see that desert-dwelling religions all practice circumcision (no water for a bath) the wearing of beards (no water for a shave) and the limiting or prohibition of alcohol (no water to replace the water you lose drinking alcohol). Jews and Muslims will defend these 'religious' beliefs which are actually just survival tactics for living in the desert
At the end of the day, the central teachings of the Bible are all pretty solid rules for living a good life: don't bang your neighbor's wife, don't kill people, don't steal shit. And this is from a former preachy annoying atheist who now is just a quiet condescending atheist.
It can be used against Christian morality in a debate on religion (this thread or post isn't, just saying) because they claim to get their morals from a book that condones slavery, ****, and the beating of women and murder of gay people, which is highly immoral, thus their source of morality in and of itself is highly immoral.
Also, the "central teachings" cross over many volumes riddled with murder, ****, slavery, stoning your children to death, and quite a few other horrific things. The Christian novels are some of the very worst moral codes a human being can go by, including eternal torture and suffering for people who commit finite crimes, which is also highly immoral.