Are they right?
I don't believe they are. In fact, I believe the Old Testament shows just the opposite and displays a God who loves, warns, and eventually carries out justice on those societies who disregard what is morally right.
To help support my position, I've written a paper that you can read on the Christian Apologetics Research Ministries (CARM) site, and also put it into presentation format below. For a deeper treatment of the paper, you can obtain a copy of Paul Copan's book that covers the subject in much more detail.