You make good points. The problem is, you're ignoring history by thinking that technology has changed anything. There is nothing new about copyrights, patents, etc. These systems have been in place for centuries, and the debates about their value have been going on for centuries (and apparently, the pro-copyright faction are winning). Technology hasen't changed anything except to make the problem "bigger".

You're right when you say: "copyright is about forbidding you from sharing what you bought with others who didn't buy it. That's much more debatable." But most people who talk about these issues don't realize that all of these things have been debated for a long time. Most people don't add anything new to the discussion, and are woefully ignorant of the thought that's already been put in.

Sources: Read, for example, Eric Flint's writing on the subject http://www.ericflint.net/index.php/2011/09/26/salvos-against...