Actually, extremists of all religions will go out and seek retribution against those they think to be foes of their religion. The JDL was particularly notorious in the 80's for this and was listed as a domestic terrorist organization in the US. Just this year the a CBC commentator denounced the local chapter of the JDL as a terrorist organization too, though the CBC subsequently retracted that statement and apologized.
Certain fundamentalist Jewish groups in Israel are just as extreme (beatings, bombings, etc) against those they believe to be Christian missionaries as are certain fundamentalist groups in Egypt against those they see as being Christian missionaries in Egypt. Others have published books approved by high-profile government-paid rabbis that argue when it is ok to kill gentiles. Apparently according to these rabbis, it's ok to kill even a gentile baby if that baby might grow up to be a threat to Jews.
Go back and look at IRA vs the Orange Order and the UDA in Northern Ireland. Sure, some of that was due to the politics of self-determination on either side, but the religious component was the driving force behind most of the terrorism and violence there.
The latest terrorist attack in Norway was a Christian nutjob trying to make a statement against Islamic inroads in what should be historically Christian Norway. I guess he forgot Norway's ancient pagan heritage of the Norse.
In particular, Christian groups have been quite willing to use terrorism and violence against what they see as the devil's abortion clinics or other threats against God in the US. Many of the patriot militia groups in the US are very heavily Christian-driven.
Hindus have their terrorist groups, as do Sikhs. In any group large enough, there will be enough nutjobs to gain the notice of the public.
Islam is arguably the fastest growing religion these days while practising Christians are in decline, and that makes them a threat to those who care about the Christina religion. The result is plenty of incentive to view Islam as threat to "our way of life" and to write about Islam as being either a serious threat, or an abomination, or both. The logical follow-on is for the more extreme Muslims to react accordingly. Given that there are a lot of Muslims in the world, it only takes a tiny percentage of that large and growing body to paint the rest as being something they are not.