Having one in 650 visitors pay for the book doesn’t seem too bad, to my mind. Especially as they’re voluntarily paying for access rather than having a copy of their own. The site could vanish tomorrow, and no-one who paid would have a copy of the book.
For the rest of us, well, I just did the equivalent of leafing through the book in the bookshop to see if there was anything that appealed to me enough to buy it. If I had to pay for every book I picked up in a bookshop, I would have even less room in my flat, and be even less able to find the books I want to read.
