'I am completely open minded about religious people instructing their children as they wish - what I am not open minded about is them wishing to instruct my children too.' I am pissed off with this assumption that all RE teachers are religious; we are not. I am an agnostic verging on the atheist, and incredibly cynical about religion. However, it fascinates me that people believe in it and the extent to which it influences laws, moral decisions, drives the political agenda, affects the rights of women, dictates how some people dress, and what they eat, and affects their behaviour. I chose to study it, and trained to teach it after 10 years, because academically it is interesting to me.
Seeker - go to an RE lesson, they will be studying Christianity, Judaism, Islam, Hinduism, Buddhism or Sikhism. I've taught all 6. At GCSE, as explained earlier, but you seem to wish to ignore this, they will be looking at what Christianity/Islam/whatever the chosen religion is, believes about a topic and why.
As for non-religious ethics, we look at utilitarianism and Kant at AS. Lower down, we discuss it and the students tell me they are influenced and make their decisions on the basis of will their action cause hurt/injury; do they care if it will?; would they like it done to them?; what it says in the media; what the view is in their home; possible consequences; we touch on situation ethics, how can one decide what the most loving thing is.
Fennel, if you look at how the timetabling is done, at KS3 my students got 3 lessons each of history and geography over a two week timetable (so 6 in total). They had 1 lesson a week of RE. At KS4, the RE short course was 1 hour a week. History and geography were options, but they had to take one of them at least, and the timetabling for those were still 4-5 lessons a fortnight, so RE doesn't detract from those. You are teaching a syllabus, and if that is the time it needs, that is what is allocated.