(For previous posts in this series, see here.)
The most basic problem with almost any religion is the fact that they raise ‘faith’, which is the irrational acceptance of things in the absence of, or even counter to, credible evidence and reason, to the level of a virtue. This is simply asking for trouble. Once you have said that you believe something just because some book says so or some inner voice tells you to do so, you have lost all standing to condemn others whose own inner voices (or the voices of their priests, rabbis, or imams) tell them to do unspeakable acts in the name of obeying god’s will.