As I said, I am an optimist
Having said that, here is my argument-
The internet disseminates all ideas including those that would normally be difficult to access. so everyone is exposed to pros and cons and differing opinions on everything. Any person can choose to self select extremist ISIS type viewpoint or they could listen to say Richard Dawkins or Christopher Hitchens or new age Deepak Chopra type figures. Some of these ideas like those of say Richard Dawkins, many people would not have had access to in a traditional conservative family, ( in mAny communities you are not allowed to question core beliefs however irrational) however these well argued debates are freely available on the internet and would make an impression on some people, perhaps those who are more intelligent or imaginative at first.
Slowly but inevitably good arguments win over bad ones.
Well argued but revolutionary ideas slowly eat at the traditional setup and society changes towards a more scientific way of thought because medieval ideas depend on faith not on rationality. ( For example it is increasingly difficult for Saudi to keep women from driving because their women through technology can see that millions of women around the world drive without any ill effects).
Once society changes and becomes more rational, it becomes more and more unacceptable to have extremist ideas like those of ISIS - slow process - at least one or two generations maybe longer.