He's not using words to analyze the ideology but to persuade people to take action (I guess -- it's hard to tell with Kerry, and he doesn't seem like the type who could get people together to do anything).
Assuming we want to get some kind of coalition together to deal with ISIS/ISIL (and once again it's hard to tell if that's what the administration really wants to do), he's not going to attack Islam or encourage others to do so or make an analysis that would damage the hopes of bringing the countries of the region and the world onboard whatever coalition we may be trying to put together.
So cherish your freedom to opine as much as you want for as long as you want, but please don't assume that government officials will exercise the same freedom.
I agree with you. In my capacity as a private opinionator, I can and do point out that Islam has a tendency to awaken the psychotic mass murderer in a person. But if I were Secretary of State trying to cobble together a coalition of muslims to go and get ISIS, I would do just as he is doing (and just as Bush did in his day) which is to try and drive a theological wedge between our allies and our enemies.
There really isn’t much of a theological bright line between “moderate” muslims and nutball psychotic muslims, but I would try to create one.