I knew very little prior to the doco - so although I probably come across as a little naive, I can also provide an un-biased fresh pair of eyes on that one programme in particular.
What you have said in your post about the police on the ground, and at senior levels, is 100% exactly what the documentary portrayed in my opinion, so your post really just re-enforces that for me - I never for any second got the idea that all police were arseholes.