Hi William,
I understand your point of view here, although I'm not at all familiar with film scoring and the ins and outs of it. As far as I can have an opinion on this topic, I know that certain films are based upon classical music (A Clockwork Orange,...) But I suppose the composer and the producer have been so honest to mention that in the credits. What you mean is the total absence of record of the true composer(s). Sometimes I use classical fragments in my works too (Pierlala has a short quote of Auber's opera "La muette de Portici", because that's an essential step in the history of my country. A particular aria was even the direct cause for the independency.) Of course I mention it in the description of the composition. I reworked the fragment to make it fit into the context and to connect it to the rest. No plagiarism this way. The main theme is a folk tune, used as a base for further elaboration. No plagiarism again. Both themes are duty free (public domain) and can be inserted freely. Of course they must be mentioned in the perspective of intellectual honesty and correctness.
Stealing somebody else's compositions to one's own benifit is a deplorible practice and far from being authentic or honest. That a composer lowers himself to do so is despicable, but that the film company or the producer accept that, is absolutely horrible. They simply must have unscrupously turned a blind eye to let this happen!
Jos