I know much of MN is quite frequently anti- faith schools, but I think what people tend to forget that whilst white, North European society is moving towards what's been termed post-Christian, the rest of the world - especially the Islamic world - is most certainly not. In fact, in many places, Islamic revivalism - associated with sects like eg Deobandism and Wahabism - is in the ascendancy, and has been since the late 70s.
So I don't think this can be divorced from religion - and surely it's better to have faith schools (which doesn't mean only children of one faith or, indeed, none) where students are taught about different religions (as they are even in church schools) learning alongside people from differing faiths? Wouldn't that improve knowledge, integration and understanding?
Otherwise as PP have said, increasing ghettoisation and catchment areas etc increase the likelihood of "faith at the weekend" dominating and no other narratives being heard as a result. Think, for example, about Tower Hamlets, and other boroughs which are heavily one faith above the others.
In Slough and roundabout, faith schools are prized by the Islamic, Sikh and Hindu communities, not because they're desperate for their children to be Anglicans when they grow up, but because they are perceived to have higher standards and better discipline. Likewise, in India and Pakistan, it's not uncommon for non-Christians to send their children to faith schools, as some have an old history and are English medium. Not all religious minorities are as vehemently anti- faith schools as some Christians/agnostics/atheists in the UK are. And a large part of that is the acceptance of a major role for religion in public life, I think.
I think - like the Saudi connection - it's mostly a red herring in terms of the problem in the UK.