As you should know by now, Wikipedia is a free-licensed encyclopedia with a restrictive image use policy. It states: images on Wikipedia should be freely licensed, with only very limited exceptions. For example, including album covers on the article about said album.
However, there is a minority viewpoint among Wikipedians that holds Wikipedia should not allow any copyrighted images whatsoever, and that doing so forfeits its claim to be a "free" encyclopedia. It's an extremist viewpoint that lost out long ago. However, the ideal it espouses is useful to understanding Wikipedia editors' view of copyrights. It also has a clever parable explaining it.
Thus the "Veganism parable" which imagines a "Vegan Potluck Dinner Anyone Can Contribute To" which is ruined when someone brings a big plate of fried chicken. Why is there fried chicken? The imagined excuses mirror Wikipedia's copyright allowances, which make for an illuminating and amusing read.