Use as Much Accurate Information as Possible
The use of accurate information in a documentary is more likely to influence an audience.
People often think that disinformation, for example, is about making up complete lies.
But actually, disinformation campaigns stress the use of incorporating as much accurate information as possible.
80% fact with 20% propaganda.
Likewise, with documentary films, you're going to have your facts and your opinions.
If you're seeking to influence an audience, I suggest using as much accurate information as possible... and slipping in about 20% of running time for your propaganda.
If you're trying to achieve a poetic resonance - like Werner Herzog does in his documentaries - this formula also applies.
For example, in "Grizzly Man."
This documentary is heavily based on fact.
Yet, 10% of the movie is left to Herzog's poetic stylization.
This dreamy mixture of 80% fact / 20% poetry in a documentary creates a pleasurable, transcendent viewing experience.