@InfraBlue,
You mean they could be counter-productive? Yes. It could break the 'allure' of ISIS. I've heard interviews of a foreigner (French) ISIS fighter complaining bitterly about their leaders. In a calm but angry voice, his face hidden, he was saying that far too many foreign fighters were sent to their death at the hands of the kurdish peshmergeh in that town where they fought for months (name?), because the bosses saw it as a symbol, that foreign fighters were treated as expandable cannon fodder... It sounded convincing. According to another source, some of the foreigners returning to Europe would be disgusted and traumatized by the sheer level of random violence they witnessed... If true, they talk to their siblings about it.