Remember that music has the power to manipulate emotionally and therefore alter the perception and eventually opinion of the audience. Very often this happens even on a subconscious level for the audience. This is why music has and is being used extensively on propaganda movies. So, while this can be a great tool, it also puts a bit of responsibility on the composer’s shoulders.
As long as things stay fictional, such manipulation is often wanted and sometimes even neccessary to “sell” the exotic locations/worlds sometimes depicted in fictional movies to the audience. But as soon as you’re scratching the surface of scoring real life events, especially on socially critical or political documentaries, you should radically tone down anything emotionally manipualtive.
Many people are quite aware nowadays when they get manipulated and simply shut off completely for the messages transported by the movie (and eventually they will hate the movie for trying to manipulate) while others will react on that manipulation. While this may sound a little dramatic, but especially with emotionally manipulating music, you’re undermining their chance to make up their own mind about what the movie tries to say by clouding their perception with emotionality.
Most likely the filmmaker/director will stop you anyway from going that path as he/she will probably want that the audience have their opinions on the arguments presented by the movie rather than emotional manipulation. On the other hand, just very few documentaries are completely free from attempts to manipulate. So be really careful about what your music is doing in any documentaries or movies with a documentary style.
As a side note: “feel-good” documentaries, like most animal documentaries that live from big landscape shots etc. are an exception of that. They can very often be approached with a quite filmic and opulent musical language and “emotional guidance” by the music might be suitable.