The problem with YouTube, and indeed a lot of TV programmes, was neatly demonstrated by an American teen called Nathan Zohner in 1997 when, aged 14, he won his school's science fair by lecturing his classmates on a dangerous chemical called Dihydrogen Monoxide.
He explained to his class, at length, that DHMO inhalation causes thousands of deaths every year, that it can cause severe, in some cases fatal, burns, that it's a major constituent of acid rain, it exacerbates the greenhouse effect and now so endemic that every river in the US has at least trace amounts of it, often much more.
He went on to explain that it's used in the distribution of pesticides and that even after washing fruit and vegetables will still be contaminated by it.
In spite of all of this DHMO is still widely used in industry, often as a coolant, but can even be found in the food industry and the US government has taken no action to stop or limit its use or distribution.
At the end of his presentation Zohner put to a vote the proposition that the US government should ban the sale and use of DHMO. The proposition won support from 86% of his classmates, with 12% undecided and only 2% voting against the proposition.
Zohner's project was entitled, "How gullible are we?" and although everything he said was absolutely factually true he had convinced 86% of his peers to try to outlaw water.
And so with YouTube, every time you watch a video there you've got no idea if watching somebody who is doing their very best to present a balanced view, or who has carefully sifted through the evidence to find that which supports their own view and is presenting it the manner most beneficial to them.
As another great example, if you've got time to do some reading, have a look at
Phil Plait's Bad Astronomy blog going through a Fox TV 'documentary' examining if the moon landings were a hoax.
Plait is a good science writer and, as you'll see from the eidts on the page, scrupulously honest about admitting his own errors and mistakes, but if you watched the documentary without his knowledge you might well reach the end feeling that the evidence that moon-landings were a hoax is overwhelming.