Humans can be strange and cruel like that.

They say nothing brings people together like love or hate. To keep the togetherness spirit going sometimes that love or hate may become more extreme over time. That is how churches, mosques, etc. splinter off over time, as some factions become more extreme than others, as a backlash to changes in society. Televangelists from America's south are a good example from the 80s, as well as some mega churches.
Radical Islam may not be the proper term - religious and ethnic fundamentalists is a better one. Throughout history Christianity has shown it's darker side, as have countless other religions. There have been many instances in the past where certain ethnicities, tribes, and religions, have displayed their dark side. Is the KKK not a terrorist organization that singles out blacks and carries out attacks and murder solely based on a person's color?
Are we not witnessing a deep and bloody hate between different tribes in Africa (Sudan) these days?

The bottom line is, if you believe some of the kids in your school are becoming dangerous, regardless of their skin color or ethnicity, you are entitled to do something about it (file a complaint/report).