I'm new here, so perhaps you could elaborate on this: What if the RCC were to teach it's kids that AIDS isn't caused by HIV? Or that homosexuality is 'unnatural'? Or that people 'exist' before they're conceived? Would fighting that fall within the remit of the BCSE? I'm not sure that the BCSE shouldn't take a more catholic perspective* on defending science education as being properly restricted to science, or on challenging unevidenced claims about reality made in other classrooms.
Not quite sure where you've got your ideas about british state schools from Made of Stars. Firstly the RCC is an, unfortunately huge, international organisation. How it operates is different in each country. Hence what it overtly and widely pushes to its followers depends on how much it can get away with and still retain customers. So in England it tends to keep as low a profile as possible on the above if it can-though sometimes it can't as in the recent adoption legislation. Also I don't think, for all it's many wrongs, the RCC has ever suggested AIDs isn't caused by HIV has it?
Secondly you seem to be confusing the RCC in general with RC schoolsand what they actually teach in England. No sane science or RE teacher would teach your AIDs assertion-if they did they'd rightly be investigated-it doesn't really require something like bcse to deal with that rather minimal threat. It shouldn't exist and if it does it should be dealt with by the mental health services. You can't really set up a body to guard against the threat of the occassionaly insane teacher.
I don't know what your experience of catholic schools is but they used to be largely 'dire' and very catholic relying, I suspect, on massive immigration from ultra catholic Ireland to fill them. Second and third generation Irish like myself were not brought up in an ultra catholic country. Hence were less indoctrinated and with less of a perceived need to send our own kids to catholic schools. Catholics, whether practising or lapsed, started to choose schools for educational rather than religious reasons. RC schools had to adapt very quickly to survive. Most did so by becoming less 'catholic' and more academic. The more they focused on education and exam results the less they focused on the extremes of RCism. Also they and their teachers exist/have been brought up in this culture not some catholic, backward one. So neither the parents nor the teachers will be taking the blindest bit of notice of all/any of the RCCs teachings on things like morals, divorce or contraception. The schools therefore would be rather foolish to do so when they compete for pupils in the market place. They tend to push the more benign aspects of catholicism (charity etc), rightly or wrongly, rather than its more evil side.
I suspect teaching that homosexuality is 'unnatural' is a breach of equality laws but would have to check. The unfortunate opt out for SRE given to faith schools allowed them to avoid mention if they chose, but I'm not sure it would have made homophobic bullying by schools acceptable. In addition I don't know a single parent, catholic or otherwise who would be happy in this day and age for their child to be told that. There are religious extremists unfortunately but they come from all sects. I suspect the more extreme, fundamentalist sects like independent baptists would be more likely to be overly homophobic and concerned with it due to their obsessions with the old testament.
And at the end of the day it is not a specifically scientific claim either, therefore wouldn't really be an issue for science education. Nor could it realistically be presented as scientific even if a lunatic homophobe managed to sneak in to schools, so I'm not sure why you think bcse should deal with it?
Organised homophobia is not yet an obvious threat to education in the way creationism is. There are no organisations trying to sneak it into schools in the way that we have creationist ones like TiS.
I've never heard the notion of people existing before they are conceived? What do you mean by this? As it is a bizarre claim I doubt it would crop up in any sane science or RE teachers class. Hence not sure how it is a science issue. If it is, as Jon suggests, to do with contraception, The RC schools I know of teach kids about the various methods of contraception both in science and SRE. As an issue I doubt it would be discussed in RE as wrong either without a fair few parents getting upset.
Again it isn't really a scientific issue, so not sure how it would in any way come under the remit of bcse?
creationism is clearly unscientific nonsense, proven incorrect again and again. Unlike personal beliefs its not a matter of opinion. It is also becoming real threat. Hence the existence of bcse. Whatever your personal issues with RCC or religion are, nothing you have cited really has anything to do with fact or science education.