I've seen plenty of atheists criticize the old testament because it supposedly supports slavery. Ephesians 6:5 and Colossians 3:22 - call on slaves to be obedient to their masters. The problem with most atheists is that they don't know the original text and translation problems. In ancient Hebrew, the word "eved" was often used to refer to a servant or a worker who was owned by someone else not a slave. Writer Paul Copan says that the word eved should not be translated into slavery.