I suppose this question is really one that asks how much of the holy books do people read. In many religions, members are discouraged from reading the text any more than that which they hear in religious services - often on the grounds they would not be able to interpret the text correctly. Oddly this applies to Muslims as well as to Christians.
Christians are often sheltered from the bad parts of the bible and only the nice happy parts are read in church and in bible studies. Muslims, whilst often having to memorise the Qur'an, only do so in Arabic and not a language that they understand. They are often told to take any teaching from sermons and, in any event, can't read the Qur'an.
It is quite clear from treading any of the holy books that there are some dreadful passages and some truly bad teachings yet most religious people have either never read these or have 'conveniently' forgotten them. However, the worse thing we see is religious people who deny their religion has either a violent past or a violent present when it is clear that their holy books sanction such violence.