It's not that he's saying it's a 'bad' religion with some fucked up rules when it's adhered to passionately. I don't think anyone can dispute that (though I think we've made some good arguments about that being true of many religions).

It's the idea that everyone who belongs to that religion is by default dangerous until proven otherwise and shouldn't be allowed to emigrate here, and that if they are allowed, they'll breed like rabbits and take over and turn the UK into a theocracy. It's just such paranoid babble.