Franklin Community Credit Union scandal is a good example, well outlined in this youtuber's (admittedly dramatized) video: https://www.youtube.com/watch?v=F0yIGG-taFI

Here are some examples from which you can extrapolate the more serious cases: https://en.wikipedia.org/wiki/Wikipedia:Lamest_edit_wars

I thought about giving examples because I understand why people would ask for them, but I decided very deliberately not to give any. It would inevitably turn into a flame war about the politics/ethics of the specific examples and distract from the reasons why I no longer trust Wikipedia.

I understand that this is unsatisfactory, but the only way to "prove" that the motivations of the people contributing to Wikipedia have shifted would be to run a systematic study for which I have neither the time nor the skills nor indeed the motivation.

Perhaps I should say that am a politically centrist person whose main interests are outside of politics.