All religions have them...

There are extremists in all religions, from Kach and Kahane Chai for Judaism, IRA, neo-nazi, KKK, other hate groups (whether they be right or left) American militant groups are Christian groups and then we have the some Islamic groups like Islamic Jihad, al-Qaeda and other various splinter groups. Shiv Sena for Hindus... I could go on and on.

The point is that these groups are, extreme, and there for by definition cannot speak for their supposed respective religions or cultures. To claim one religion is more violent over the other is ethnocentric.