This is something Jerry Pournelle used to complain about. He edited some pages relating to the US space program. Events in which he took part or knew the people involved. Then he'd come back a month later and find the page had been edited again with the incorrect information re-inserted. Eventually he just gave up.

And then there are political problems. The Tyson affair is a good example - Neil deGrasse Tyson spent many years spouting made-up quotes supposedly uttered by political opponents (Like this one, for instance - https://www.youtube.com/watch?v=h_jG5kKfacY). Eventually someone compiled all the nonsense and it was something of a mini-scandal. The wiki editors refused to allow any mention of it on his page, so the whole affair is mostly down the memory hole now, just like they intended.

Wikipedia is good for historical references (pre 1900 or so), and a good place to start if you just don't know anything about the thing you're looking up. But to rely on it for anything that's the slightest bit controversial is daft.