These people are evil, and any and all claims they have that they are righteous and just are voided by their own actions and creed.
ISIS are generally quite self-affirming, so not by their creed in the sense of them having problems with their own actions, which they generally do not. In the sense that they are inherently 'evil' according to the popular morality of nations which were opposed to them, then yes, but that was to be expected during a war.
I say stick them in prison or put them through some kind of mental rehabilitation.
As most countries who might have tried such were also at war with ISIS, somehow or other, 'mental rehabilitation' would merely be propagandising on their own part, and probably not something they would wish to be too closely associated with. It was perhaps more suited to domestic issues which were not (yet) organised into an opposed force.
It might also cheapen attempts to portray them as exclusive users of 'brainwashing.'
And if they don't think change will happen then oh well they can all move somewhere else where people like them.
Presumably their problem is with the resentment against their religion in principle, not just the personal inconvenience that it might cause them. They aren't just going to leave it unopposed, as if they didn't actually believe in their own religion.
If a given nation was systematically opposed to central principles of their religion, they would ultimately find themselves in opposition to it, and the general system which it represented. Unlike much of Christianity, it was not of course a politically neutral or passive religion, which would even if they wished for a system to be overthrown ignore them or seek to compromise with them and then alter their religion in accordance. It would hence be either ostracised anyway, or organise against this in whatever form, either one attempting to compromise and please the West in some way, or one which subverted its popular values. In any case it would not be appealing to them.
The majority of Islamic people also condemn ISIS, so how is it due to their ill treatment that spurs them to join ISIS when it's the extremely small minority that actually go to Syria for the sake of jihad.
Muslims come in many forms. Catholicism, of course, emulated the behaviour of multinationals far before their time by killing the Cathars for really very little reason, but nonetheless is still proclaimed the true church as opposed to such religious outgrowths, in part because it is 'established' or in brief because of such actions. Christians stand firmly opposed to such things elsewhere, as in Protestantism, and people like Kierkegaard took issue with Protestantism while still standing apart from Catholicism, while there were also some other earlier sects that died out when catholicism was integrated into the Roman Empire. With Muslims, such differentiation is only hidden in part because it is a religion active on a political level - politicians often only give lip service to Christianity anyway, another sense in which mandating that people follow Islam in a way that they consider 'correct' was only likely to be alienating and engender antagonism - and hence tended to collapse into on the one hand 'integrated' Muslims, who were generally in harmony with Western values and did not proclaim their overthrow, etc., and were generally speaking characterised as an undifferentiated mass of 'supporters' by the non-Muslim West and were frequently quite happy to go along with this characterisation, and on the other hand tendencies like ISIS who opposed the West and hence had its citizens urged against this by their government, through several media. The more the former hustled together and became similar, as a form of resistance of some sort, the more people who were not incorporated into such, such as radical preachers, were increasingly moved into the side represented by ISIS, etc., and probably suspicious of those who would support the US and its values over ISIS in a war situation. Because of Israel, they also had a reason to be suspicious of those who had Western support or supported the West generally, which could easily be associated with their other opposition who bore the stamp of the Western nations. Certainly, being reconciled with such powers as had and continued to have a significant level of indifference or despite for Muslims, or presumed to dictate their own religion from a secular, pseudo-Christian viewpoint, would generally be uneasy, and in that sense the Western governments had little persuasive power in such regions short of submission.
Of course, Western governments were democratic, and hence politicians were such as were deeply concerned about, validated and valued what anyone had to say, of any sort, while the Muslims were more focussed. As such, the West's being unable to persuade opposition, despite their position in the world system, must have rankled.
In this case maybe the best idea is what Riko said, have them be educated correctly and thoroughly on what their religion teaches.
If you tried a similar thing with Christianity, this would generally come across as quite farcical - as if most Christians are without controversy orthodox on all matters - and if it comes across elsewise, it is only because Islam was treated less as a religion than a problem and opposition to be solved. This kind of approach was also manifested in the Middle East in part, where the displacement of Islamic nations by a pseudo-racial 'Jewish' state was treated as a matter of course.
Is a Christian or secular - that is, distanced from religion in some way - state going to monitor every religion, including Judaism, for whether or not it is 'correct'? Especially given, of course, that most religions don't even attempt to abide strictly by their earlier texts, and often feel the need to go further than them, or tone them down to fit into modernity and be less inimical to other religions.
Regardless, there is no excuse for joining any terrorist group. The worst part of it is that a lot of these young men end up losing their lives.
Propagating the not-quite-official war on Iraq was something that the state of the US sponsored with not little enthusiasm recently, often despite dubious causes. They hardly had that much room for shock about this kind of thing in citizens.
Even though locking them up is for the benefit of both themselves and the country, there is always the chance of IS turning them into martyrs for their recruiting campaigns, painting us as the bad guys.
It's unlikely to benefit their purpose, or them in terms of why they act generally, so perhaps as some abstract, inert being who is merely a hypothesis, and was open to such 'help' in integration. That said, if ISIS can portray people as martyrs for being imprisoned, for instance, that bespeaks a high degree of solidarity with their global supporters.
