Underscoring -- a contrary view

The trend after about 1935 toward more and more symphonic underscoring had its persistent critics, who objected not only to the idea of musical commentary (underscoring as analogous to the voice-over narrator) but also to music's use when emotionally or dramatically redundant. Kurt London (Film Music, 1936), for example, minces no words on the subject:

Just as once the sound-film song hit ruined the whole structure of many films, so now a pernicious habit of 'mixing' music behind a scene, without any particular motive or connection, has already had quite a number of unpleasant consequences. To give an example. A pair of lovers speak of their feelings for one another; or a tearful parting is enacted; or a dead man is being mourned. Suddenly—no one can tell why—a violin starts sighing out some tearful phrase. Result —a terrible strain on the lachrymal glands. It is an abuse of music to obtain with it a dramatic effect which should be achieved in any case, provided the situation be well founded, well acted, and well staged. 

This vulgar straining after effect has unfortunately become noticeable even in big films, in scenes, moreover, where there could be no possible justification for it [and] it has recently spread with painful rapidity.  

There are in reality only a very few occasions which would justify a use of 'illustrative' background music; still less, a mixture of speech, music, and noises. The dangers of background music are indeed very great.