This is why:
And if you now find yourself sitting atop a high horse saying “hey wait a minute, my religion’s different, we’re peaceful. We don’t behave like that” – you’ve just witnessed a snapshot of Christianity from as late as around 400 years ago, so you don’t get out of it as easily as that. You’re all as bad as each other; some at least are more open about it.
My favourite quotable atheist said it best…
“They knew no better, but I do not propose to follow the example of a barbarian because he was honestly a barbarian.”
— Colonel Robert Green Ingersoll, The Limitations of Toleration (1888)