To play devil's advocate for a short while, the issue is one of personal identity. Even for second generation migrants, hell, especially for second generation migrants the concept of 'home' and their identity often lies between the two. Now the issue isn't that they are Muslims here. A second generation migrant from Iraq might have some very vocal views about the Iraq war and might be a target for radicalisation as a result. Some Muslims might similarly see violence against middle eastern states as an attack on their identity while the region itself might have very different views.
It's a pretty complex issue.
And like I said, they can have a variety of opinions on UK foreign policy but the idea that curtailing x or y foreign policy decision as a means to address young men committing mass murder is a little ludicrous to me. Doubly so when most of the people ISIS ultimately kills are other muslims.