I believe we must before anything else distinguish (and it is hard and personal) from themes-motifs and themes-melodies. On a general point, I have to disagree with one of Paul's examples; Goldsmith to my mind is very much a theme-based composer - all his scores that come to mind are very much based on strong themes, but he wasn't always great at them, it was a matter of hard work for him many times; you can tell how a lot of his themes are "forced" in a way, having a theme because one has to sort of thing (ex. Supergirl, Lionheart, etc.) - that of course can be the result of accepting 200 contracts a year for money - how many themes does one have in him? However, his themes (and most are themes-melodies) for say Papillon, Chinatown, Star Trek TMP, Patton, Omen, Final Conflict, Patch of Blue, Under Fire, the list goes on..., range from inspired to incredible.
However Paul is very right pointing out that themes are not mandatory for the setting of a film, but the difference froom today's tardies is that (among other things) Herrmann could certainly weave a theme, wistful or playful (ex. Vertigo theme2, The Trouble with Harry), and of course he had all the other arsenal in abundance if say themes were not his strongest suit. John Williams is another composer who in my opinion is great with everything, including great themes-motifs, but should (and does for the most part) shy away from themes-melodies (yes, it's very true, I find the scraping series of crotchets - or is it quavers - of Schindler's List very disappointing).
I won't repeat Paul's well argued points on how capable composers can decide on how to impressively and resultoriously put music to cinematic drama whether they work with motifs (Williams, Bernstein, Elfman) or melodies (the Italians, Barry, Jarre), but I do want to repeat one aspect he brings up, and that is the perils of the so-called objective discussion that supposedly cannot be had because of those twits that insist their opinions and aesthetics are as valid as anyone else's. What these twirps confuse, is their undeniable right for personal preference, and the intellectual and repertorial backgrounds necessary to make those preferences.
For example, for people to argue whether Bach or Beethoven is the greatest ever composer, is a valid discussion with subjective commentary and preference, albeit based on objective truths and foundations.
To say Madonna is a greater melodist than Mozart, is a subjective preference, but based on subjective i g n o r a n c e. Your every day pleb "thinks" that because everything eventually and necessarily boils down to personal preference, that means there can be no objectivity in the parameters set for any discussion on aesthetics.