fundamentalism is an issue that is compounded by organized groups, yes but they don't have to be exclusively religious. they can also be political.
They
can, but more often then not, they aren't.
Note also that poltics for the fundamentalists, is pretty much the same thing as the religious beliefs.
cfr "political islam", or the "politics" behind prohibiting abortion or same sex marriage.
Politics is, in the end, an
extension and/or
implementation of underlying philosophical and/or religious beliefs.
In my case, my political ideas will be heavily influenced by my ideas concerning humanism and alike.
In ISIS case, their politics is completely engulfed by islamist religious beliefs.
In certain conservatives in the US, their politics are influenced by radical christianity.
They don't argue agains abortion or same-sex marriage because of real-world argumentation and data... they are rather against it because of underlying religious beliefs.
And to come full circle on this, this is
exactly why radical religious beliefs are so dangerous, especially when it concerns politicians..