Wikipedia, Google Books, and the Pirate Bay have trained many people to expect that knowledge should always be zero-cost. I used to feel that way, too.

I feel like this is an important point - knowledge is worth paying for, and anything worth paying for is worth getting for free (given that the costs associated with getting it for free don't outweigh the cost of paying for it in the first place). As you rightfully point out in the quoted text, when the free sources are more comprehensive and higher quality than the paid sources, it is easy to get confused.