Back to the discussion ...
Here is the kind of liberal media debate over whether Islam promotes Violence, in response the point Bill Maher made:
http://www.salon.com/2014/09/30/reza_aslan_takes_down_bill_mahers_facile_arguments_on_islam_in_just_5_minutes/
Superficially, the points made are fine and convincing but unfortunately the hosts don't think to ask anything other than repeat the question and fail to notice that the answer isn't to the actual question asked:
Q: "Does Islam promote violence?"
A: The vast majority of muslims are not violent
That answer doesn't mean that islam doesn't promote violence, simply that the majority of people have the sense not to act on it.
But it still promotes violence and the problem is that allowing this promotion to happen is dangerous because a sizeable minority do decide to act on it and really, why should some innocent woman going to work one day have to die a horrible death, not get to say goodbye to loved ones, not get to live the years she'd planned ... all because some moron supposedly has the 'right' to promote a violent ideology to some other moron?
The argument seems to be that these were just violent people and it's not the religions fault. In which case the question should then become - "why does islam disproportionately attract people with a predisposition to extreme and graphical violence?"
It is a disease, whether every carrier succumbs to the symptoms or not - if nothing else they keep the disease alive.