There is indeed a inherently honesty to it.
It simply is not cost affective to cover stories from independent sources.
Activism could be defined as activities engaged in by individuals to change there of others situation.
The power and appeal of Documentary is the way it alters and plays with the way the viewer relates to and understands the subject.
Inherently participatory in nature, Community Video focusing on using video to enable communities to communicate amongst themselves as well as with others.
An office occupation is another example as not only douse it disrupt the activities of the organization it also can raise the media profile of the campaign.
Indeed it can be argued that to make a powerful film you must care about the subject, therefore powerful films tend to be both political and partisan in nature.
There is also an artistic element which is lead by the film maker. Issues of what is reality and objectivity are as always relevant as someone is going to edit the film.
Due to the political nature of film, partisan film making, especially where the subject is close to the film makers hart, tend to be the norm, rather than the exception.
This is indeed not only relevant to Documentary but is evident is most type of film making. The film often mirrors the experience, understanding and politics of the director.