I entirely understand your position. I for one am deeply disturbed at recent efforts to "normalise" paedophilia (various horrid TED talk type speeches saying it's just another form of sexual expression, etc), and having children of my own, it is safe to say that for all my liberal credentials, things would get medieval very quickly if a paedophile were to interfere with one of my children, nephews, nieces, etc.
All that said, I have a couple of questions for you, because I'm curious:
Would you feel less vehement about a film like Cuties if it were shot-for-shot as it is today, but with over 18s made to look 12, etc?
How do you feel about "natural" nudity in films when it comes to children? The BBFC have no restrictions on this, even at the U category. That's why historically you've had films like Walkabout passed with no questions. Or films like The Mission (which features South American tribes). Or that nude shot with the mother/son at the start of Clash of the Titans. Or even that brief shot in Superman, which hadn't even occurred to me as being potentially problematic until someone pointed it out to me the other day.
Quite honestly, with the above four films (all of which have been favourites since childhood or early teenage years), I've never batted an eyelid (though I admit the first time I saw Walkabout at around thirteen, I developed a serious teenage obsession with Jenny Agutter).
Then again, I'm not sure such decisions would be taken in today's climate. I doubt a film like Walkabout could be made today, and Jenny Agutter has said, in interviews, that the internet has seen to that (because they wouldn't have made the film the way they did if they had anticipated the internet - she was seventeen when the film was shot, by the way).