Law and reason

A reader asked for a clarification on what Archbishop of Canterbury Rowan Williams said last week, and why it matters. The earliest reference I was able to hunt down quickly was this one from the Telegraph, but the comments were made in a radio address.
This became a big controversy because of the number of Muslims who have immigrated to England in recent decades and years and who have not assimilated into British society, but have tried to keep their own religion, customs, and language. A number of British fear that their legal traditions will be altered by the uncritical and wholesale adoption of distasteful aspects of Sharia, or muslim law.
This is not a new or uncommon fear. It is part of why the Mormons were persecuted in Missouri: There, the older settlers took matters into their own hands regardless of law and drove the Mormons out. American immigrants into Texas brought their own governmental preferences, culture, and language, and succeded in separating from Mexico, and joining the US, as some evidence that the fear is not entirely without foundation. Now, in the 21st century, the illegal immigration from Mexico provokes similar fears in the US.
I'm not sure that the British legal system, or the American legal system derived from it, is inherently more just in all aspects than any aspect of Muslim law. Certainly there are aspects of Sharia that are repellent. There are also aspects of American law that are unjust and repellent. If were were interested in justice as an idea more than a reflexive adherence to our own traditions, it might be well to study Sharia, compare and contrast it to American law, and see whether there is anything that it would be worthwhile to accept. On reviewing Archbishop William's comments, as close as I can come with a rather cursory search, I think this is what he is saying, and to call his comments a form of "surrender" is bit unfair.
But the whole debate has become so polarized and highly charged politically that it's hard for calm reason to have any influence.