Radical religious extremists of any ilk are capable of terrible acts in the name of their particular god or religion. This includes radical Muslims, or course, and I'd be a fool burying my head in the sand if I couldn't see that radical Islamic beliefs and practices in some parts of the world today are wreaking havoc.
Every dog has his day. Radical Christian beliefs have wreaked havoc in societies in the past. Some other wacko interpretation of religious tenets will rise in the future and wreak some more. Radical atheistic regimes killed more people in the 20th century than even seems humanly possible.
See the key word there? RADICAL. That means simply that these beliefs - and the people holding them - are not the mainstream. They are not representative of the majority of those who also claim some of the same tenets as the BASIS for their personal beliefs and practices.
To paraphrase the words of Jesus, "The radicals are with us always." To refuse to acknowledge their presence out of some sort of sense of political correctness can be very harmful.
But to assume that all followers of any particular belief system share the radicals' interpretation is also harmful.
It's a balancing act and takes mental discipline, but it's easier when we ask ourselves this:
Do we really want to be judged by the fringe elements of our own belief systems? If not, then we shouldn't be quick to judge and categorize either.