There could be couple of reasons why instinctively we think about paying for bread as a mutually beneficial exchange of goods for money, and about paying for internet articles as a "paywall that discriminates the poor":

(a) Articles used to be free, and many (in other publications) are still free.

(b) There is a very little incremental cost to WSJ if a single article will be read for free by someone, as opposed to the supermarket example above where an incremental loaf of bread has a very real economic cost.

But that doesn't change the fact the WSJ article is a real good that cost a lot of money to produce and therefore should be paid for.

edit: grammar