So are you saying the IRA and KKK are not organized groups?  Before you suggest IRA is a nationalist group, their goal was no different than Al Qaeda's - to remove the military presence and occupation of a much more powerful empire with a different religion.  Religion was the main cause of strife in Northern Ireland.   KKK is more about race, but it is not the Star of David they burn.  They may seem totally unlike the Christianity you know, but the same holds true for moderate Muslims when they view Al Qaeda.  Unless you believe once race is better than another (i.e. you are racist), it doesn't stand to reason there would be no Christian extremists. KKK is not the only white supremacist group that claims to be Christian.