One of the problems behind this, and one of the reasons it seems to be islam doing this sort of thing is because of the nature of the religious clerics.
In the main Christian churches, vicars, priests, ministers etc. go off to study. They study not just the bible, but all manner of subjects. The Vatican has a pretty decent scientific research facility for one! But, almost any Christian preacher you meet will be well educated and well rounded.
However, in Islam people like Abu Hamza can become an Imman. They don't go to a special college, they don't learn about life the universe and everything, they just learn the Qu'ran and hear another's interpretation of what the Qu'ran means.
This is a long tradition, and in years gone by a lot of Imman couldn't actually read! So, it was learned largely by chinese whispers pretty much. So, the true meaning of the Qu'ran was lost on these folk. THESE are the people who have lead to the radical sects.
The reason they believe they can go around killing people is because in THEIR interpretation of the Qu'ran (an incorrect interpretation I might add), only a muslim is a true human. To them, non-muslims are no more than animals. This is why throat-slitting seems to be quite popular amongst some (this is the halal way to kill animals for food). So, they believe that by killing us all, they are killing animals and not humans.
Of course, it defies logic: if we ARE animals, then what damage can we really do to their way of life? Would a Christian go and kill a herd of cows because they didn't accept Jesus as their saviour?
Freddie, there are bad muslims, just as there are bad Christians, bad Hindus, Sikhs, Buddhists, Shintoists, Atheists etc.
Whenever anyone brings their own religion into an argument, all they do is cheapen it.