I have to say I was shocked when Rowan Williams suggested this. I have met him briefly on a couple of occasions, and on that experience and from what I have read and seen of him, he seems to be an intelligent and thoughtful guy.
However on this occasion I think he has ended up in a blind alley. We cannot have a system in this country where it is one set of laws for one culture and another set of laws for another. It will lead to a sense of resentment and confusion and help divide the country when we need to understand and work together accross the cultural barriers that exist.
One way to do that is to help uphold the law and it's framework in a way that benefits many, if not all of it's citizens. If people have a problem with a certain law, then campaign to get it changed, but what the Archbishop says will not work and is unhelpful to all concerned