There have been plenty of killings/massacre's done by extremists of other religions; islam lately have been slandered most in the last 50 years due to immigration etc. The media talk about stories which will be popular, e.g. Paris attacks were broadcasted mainly because it's alot closer to home and unfortunately more people will care about that, than for example the lebanon bombings etc.
It is a very small % of individuals that become extremists and take their religious beliefs to the extreme and join terrorist groups, a fraction of a percenatage, and the rest of those who practice the same religion condemn their actions also.
Personally i'm an aetheist and think it's all fucking ridiculous the thing's people will do in the name of something they've only been told about and read in books, religion is the route of all evil and always has been, but unfortunately people have their own beliefs even if they are scientifically and proven to be incorrect. People just don't have common sense