I think Islam gives disillusioned youngsters (men!) a sense of belonging, especially if they are living in an alien culture (such as new immigrants to the UK).
It's far easier to follow a rule book than think for yourself.
I've plenty of Muslim friends, so don't think all Muslims are radical, but I do think those that are fundamentalist are weak and find it easier to follow what someone is telling them.
Modern (and the original) Christianity is totally different. A true Christian follows the teachings of Jesus and not a dogma laid down by a 'church'. And Jesus always encouraged free-thinking and action. And he stated that the most important teaching was 'love one another'. He didn't add 'only if they follow my teachings too'. True Christianity encourages you to question theology and question why you believe what you believe, not follow blindly.
What value does belief have if you just follow a doctrine and don't understand why you are following it? I fear that Islam stiffles free-thinking, which is, in effect, brainwashing.