The cause of ISIS is Islamic extremism. Not income inequality. Not climate change. Islamic extremism. Those who claim otherwise are merely playing politics to advance political agendas. Sam Harris, the well-known atheist author and speaker, describes such people well[0]: "These people are part of what [Muslim reformist] Maajid Nawaz has termed the “regressive Left”—pseudo-liberals who are so blinded by identity polit…
This assertion seems obviously false. ISIS isn't suddenly "better" because they are killing in the name of something other than "Islamic extremism." There are also plenty of extreme right-wing muslims who don't kill people, which also suggests that a generic diagnosis of "islamic extremism" is not enough to explain ISIS.
If you /really/ believe ISIS is powered by a fervent belief in fundamentalist Islam and nothing else, then there are no remedies other than killing every member of the group as their rhetoric inescapably leads to the conclusion they should kill everyone who disagrees with them. Of course, to believe that, you also have to believe previous groups that espoused philosophies with similar conclusions (Al' Qaeda, etc) were lying - as we haven't kill all of their members and their terrorist & militant activities have fallen off. If all muslim extremists are driven solely by personal belief in islamic extremism, we would never expect them to change their behavior.
But people do change! All the time. So, even if you believe that all extremely right-wing muslims want to kill everyone all the time (a preposition I find hard to believe myself), you should also see that some (most I would say) muslim extremists choose not to kill most of the people most of the time. If we want to save as many lives as possible we should, while we push back against the intellectual garbage of extreme Islam, should also work to understand the factors that cause some extremists to kill and others to live in relative harmony.