The Bible — aside from it’s literary value — is quite simply an incoherent basis for morality. The truth is that everyone — atheist, liberal theist, fundamentalist, whatever — uses their own moral compass to decide what they accept and what they reject. If any Bible-believing Christian tells you otherwise, just ask him or her if a rebellious teenager should be stoned to death.
The Bible makes a convenient scapegoat for some because frankly, one can base pretty much any belief on one or more more scattered fragments of scripture. That’s probably a big reason why it has survived for so long — and why Christianity has not been one single religion, but dozens, for several centuries at least. I can come up with pretty much any bullshit doctrine I care to and find some Biblical backing for it, and voila! A new sect is born.