Milly, like it or not you live your life within a set of laws that are based on the Decalogue, Judeo-Christian rules. Like it or not, religion is still a big ticket issue in the world. It affects ethics, politics and in the States, science. Whilst you may not practice religion (I don't), I still want my ds to see that belief has a huge impact on all our lives and to try to teach him why that is. I think religion is one of the main drivers of the events of the last 85 years and will continue to be so.
You cannot teach the political dimension of a topic without reference in many cases to the religious. If the woman who is sentenced to death by stoning for adultery in Iran was a topic in Crime and Punishment, how could one avoid mentioning that Iran is a Muslim country?
How do you approach the case of the doctor who was shot by an anti abortionist who was a Christian? Where do ethics come from? Aren't we all really following the Golden Rule as outlined in the NT, whether we believe in religion or not?
How can one teach the Arab/Israeli conflict without reference to the religious aspect of this? I shall be fascinated to see how ds's history teacher approaches this, later on this year.
Why don't you go to a GCSE RE lesson Milly and see what we actually do? I don't teach these things as a primarily religious concern at all. I ask the class their views on abortion as an example. Run through the history, what the law says, have a debate for and against, show a video about the issues surrounding late abortions (having issued a warning the week before so that those who would be affected can let me know they'll be absent), and only then, look at the differing views within Christianity and Judaism from the RC view of no, to the liberal protestant, lesser of two evils stance. Same with Judaism.
I would not teach GCSE Catholicism anyway, as I believe in abortion and contraception and I do not believe that any man is infallible. I also have to disagree with you here 'What offends me most about RE is that people say it is vital to teach children about diversity.' I'm not teaching about diversity, I'm teaching what the differing religions believe and showing how in many cases the beliefs are very similar, although presented in a different way and resulting in different practices. I'm trying to teach religious literacy not diversity, a very different thing imo.