And as an example of bias: I personally witnessed a wikipedia editors adding their own
interpretation of a certain written article. This interpretation was very politically biased and not justified by the text, but these were influential wikipedia editors so that it stayed in. I then
asked the author of the article on Twitter if this interpretation was correct. I was unambiguously told NO. This information (including the public twitter conversation), was rejected by the wikipedia editors because it was first hand accounts.
Which led to the rather odd result that the interpretation of an article's message by a Wikipedia editor was favoured over the explicit statement by the article's author.
Here I would have thought that it would have been prudent to simply leave out that part of speculation, but they adamantly insisted it should stay.
I must add that this happened on Swedish wikipedia, not the main English Wikipedia – which I actually found much more balanced. But the problem is that this mechanism exists in the first place.
It was at the time (5-10 years ago?) well known that the Wikipedia of some language – I don't recall which one – was at the time pretty much hijacked by a group. Oh, wait I found it - the Croatian Wikipedia.
This is unlikely to happen to the main Wikipedia, but it does demonstrate a certain brittleness and risk of bias in the system.