On this page, you learn about how technology allows for perfect copies at no cost and why that matters.
In the past, making a copy of something required a physical medium: paper, cassette tape, CD, videotape, DVD, etc. So in the old days, copyright holders didn't have to worry about individuals copying something for their friends. The cost limited the number of copies anyone would make. And before computers, copies were never perfect. So copyright holders ignored individual copying and focused on people with bulk copying facilities who sold large numbers of copies illegally.
But now anyone can post a copy of something online at zero cost, and anyone else can download or stream the content directly from the Internet. So today the big threat to copyright holders is individuals, especially when the individual posts the illegal copy on the web for many people rather than just emailing it to a few people they know personally. Therefore, without copyright, the official publisher would be competing with people who can give away copies for free.
That's a slogan that arose in the early days of the Internet, to argue against copyright. Since everyone can copy everything so easily, according to this argument, the idea of artificially restricting such copying is doomed to failure; copyright is obsolete. But technology makes copying digital media essentially free, so copyright is also more important than ever! In the old days, copying was limited by the physical cost. Now there's nothing but copyright allowing artists to support themselves, which is a legal and ethical issue.