Or, to put it another way; when answering a similar question from people of faith I will sometimes reply "because people like you used to burn people like me at the stake".
After 2000+ years of foaming-at-the-mouth theists, people get all pissy about vocal atheists like Richard Dawkins. After we've had 2000ish years of foaming-at-the-mouth atheists then - and only then - can theists justifiably complain about the likes of Prof. Dawkins. And I'll bet in 2000 years there'll still be Christians convinced that the return of Jesus is imminent. Both of them.