The problem is that the act of sharing something digitally is implicitly assumed to be making a copy wheres lending someone a book you have already read and internalized is not. Copyright laws should have been adjusted to preserve the same freedoms for digital use as you had before rather than being even more of a bad deal for society.
It's not "assumed" to be making a copy. It clearly is making a copy. Nerds like us want there to be a special kind of copy that doesn't "count" under copyright law, to facilitate things like CDL. But there isn't, and the courts are the wrong place to look for it. Go get a new Copyright Act passed.
Since this is hn, I'm going to be pedantic and somewhat offtopic. :)
There are special kinds of copies that specifically don't count under copyright law : basically anything "cached", be it in RAM, browser caches, or similar.
loading story #41500488