I've been away from Wikipedia for three years. I thought it was just a fad that would go away. Now it looks like it's here to stay, and it will continue to be a harmful influence on everyone. I'm just one man, I can't stop this disaster.
Kozierok's first law
"The apparent accuracy of a Wikipedia article is inversely proportional to the depth of the reader's knowledge of the topic." — Kozierok's First Law
For example, I know a lot about the clarinet. The Wikipedia article on the clarinet seems to me to be a mixture of bald facts, half-truths, misunderstandings and outright hoaxes.
I know next to nothing about Hopf algebra. The Wikipedia article about that looks very accurate to me.