There are doubtless many appallingly cruel and inhumane practices performed in the name of religion, and I don't think anyone here could possibly defend them. My husband's sisters and cousins were all cut in a large group one day by a horrible old woman with a rusty razor blade. He says he'll never ever forget their terrible screams of pain. I've clarified the reason for their mutilation and it seems it was for Islam (ie not a 'cultural' thing, but a 'religious' one) It's illegal now in Ivory Coast, but in the remote villages it still happens.
And there have been mass suicides by members of a cult under the spell of their religious leader. Not to mention the self-torture by 'holy men' in India. There are endless examples.
I can't speak for others, but I have a very firm idea of what I will and won't do in the name of my particular faith. (See the 'purificator' fiasco I mentioned earlier) However, many adherents are vulnerable and gullible. What mother of a young girl would agree to having the child agonisingly mutilated unless she had been completely brainwashed by the members of her religious group? Or what parents would administer deadly poison to their infants en masse unless hypnotised to the point where all normality has gone?
It is this kind of abuse which shows that religion can be a very dangerous phenomenon.