The Realities.

"It is critical that film makers bend of fantasy that dicumentary can be inproblematic representations of reality that 'truth' can be conveniently dispensed and recieved like valium."

- Dennis O'Rourke.
(Documentary Film Maker)

Reality is here and now and the truth is capturing it. This makes Truth and Reality an argument.
"To stop the argument between truth and reality, evidence should be used." - John Corner.

Documentaries show a transformed world to make things seem more interesting, however they are not rating boosters - this is what current affairs are which means that it is documentaries that are difficult to schedule.
Research also shows that the general public enjoy documentaries about Sex, Violence and Law & Order.
Controversy is not popular with TV Networks due to them going against the Government, which means that Public Service channels have more documentaries scheduled than commercial cannels.

The complex relationship between the documentaries, the people that are in them and the audience is called Triangulisation.

Documentaries are usually about societies victims (this could be a rape victim, someone who is murdered, someone convicted, etc...). This means that human beings are used as evidnece in their exposition and they can expose and exploit peoples lives.
Although this is true, documentary makers also see the right of the public to know and be aware of things that they would not otherwise be aware of - this is what makes them controversial. The makers believe that as a society, if we see something wrong, we will try and right it.
A perfect example of this was Ken Loache's 'Cathy Come Home' (1966) which lead to a change in the law about homeless people.