> Some people are upset he's making a profit.
Is that really what "some people" are upset about? That's not the impression I get either from the article or from comments here. Some people are upset that he, and others like him, are making it harder or less pleasant for them to buy used books. Some people are (something rather less than) upset because what he's doing displeases them aesthetically -- books are meant to be treated with reverence, bought and sold by people who love them, etc. But I don't see anyone saying "He's making a profit, and that's bad".
As to whether what he's doing is, on balance, beneficial or harmful, I don't think we have enough information to know for sure.
Scenario 1. A small minority of particularly good used-book shops, which would otherwise have had real trouble selling their merchandise, are visited by people like this; the result is that lots of books from their shelves are made available to people who want them, and that the booksellers stay in business. Everyone wins.
Scenario 2. All the world's used-book shops are deluged with people like this. As soon as any new books arrive they pounce on them. The result is that all the books anyone wants are sold at higher prices, reducing their availability to people with less money; and that the used-book shops no longer get any "normal" customers because most of the interesting books disappear as soon as they hit the shelves, and that after a while the booksellers give up in disgust. Everyone loses.
Presumably the truth is somewhere in between. I'd guess it's much closer to Scenario 1. But fearing Scenario 2 isn't really all that crazy.