Looking at those arrested for joining ISIS here in my home country I don't know how you can say that. They were not poor, they were not excluded or treated in a racist manner at all. And there are very little lines between them, men and women, from different parts of the country, from different backgrounds (semi-rural versus rural, native/non-native, dutch, french, english-speaking, rich/middle class (I'd say no poor people so far), ...).
About the only link between the ISIS members from Western Europe is that they're muslims. Even that is "not 100%" true, since there are also Christians and some Kurds traveling to Syria/Iraq. The examples of that I know went there to help, of course (medically in 2 cases, sort of an amateur doctors without borders, mostly because neither doctors without borders, nor the red cross risk sending people there, but they did have family there). Of course we don't know that's all they did. At least they're claiming to provide medical help, none of the muslims who got caught going to Syria ever even bothered to say they were going for any reason other than fighting, and some saying they went off for killing and some shit about allah.
This is a convicted ISIS terrorist that went off to kill people and came back, talking to a reporter of the public service about how and why : https://www.youtube.com/watch?v=yKg2UsfnxHc
Claiming that people like this are poor or treated badly by the country they were born into is moronic.
Meanwhile the tensions between (sunni) muslims and everybody, literally everybody else are rising ever more. Fights and crimes against the "natives", and every other minority, from the Jews of Antwerp to the Turks of Molenbeek (there is a large (sometimes very) atheist contingent amongst Turks).