The story of your enslavement

I suppose too if a doctor tell you that you have cancer, this is just a "pessimistic perception of life"? But does it change the fact?

Does the fact that a glass contains 50% of its total change merely because you state it as 50% empty as opposed to 50% full?

No.

If you cannot address the facts in the video and show them to be incredible or incorrect then you cannot dismiss the presentation as prejudice. Merely asserting that a fact of reality is depressing or "pessimistic" does not make it go away. Things are what they are, regardless of how you may feel about them.