[matheusmoreira]

> I'm not sure why the ability to sell $100 books for $0 (or even $10 books for $0) is a qualitative change and not merely a quantitative one.

The difference is the sheer scale of it.

Printing presses are expensive, purpose built hardware. People who had access to one were part of the industry. Enforcing copyright is much easier when infringement is centralized like this. So copyright infringement at scale wasn't that common. Also, since the books were physical copies there are natural limits to how many can be made and their widespread distribution is a hard logistical problem.

Compare that to the 21st century. Almost everyone has a computer which can create a virtually unbounded number of copies of any file. These computers are also connected to a global network which makes it trivial to distribute these copies to anyone who wants them. In the 21st century, anyone can easily infringe copyright at massive scales and it's impossible to enforce copyright in any meaningful way because infringement is decentralized among the general world population.