Well I don't really have a line, but that doesn't mean I'm going to go linking directly to such sources in public - not everyone agrees with my stance on copyright. Those who do can easily go find it themselves.

Also Macbeth was written 400 years ago. Let's not pretend this is a fair comparison. This author has been dead only 20 years - it might be that their partner is still alive and needs that money, or their children.

Why won't anyone think of the publishers and the book stores!

Amazon is hanging on by a thread, and piracy is stealing their cut.

That’s newer than Star Wars and isn’t a huge piece of IP. To the estate a few book sales makes a difference.

An obvious line would be when copyright expires. In fact, drawing that line is exactly what copyright expiry is intended to do.

What's a "sane" point at which you become entitled to other people's work?

What a strange way to phrase it, considering in your last comment you were talking about how copyright expiry is exactly for this purpose.

Anyway, what is copyright expiration in America these days? 100 years?

Also, is it simply a matter of X years after creation? I somehow doubt it's that simple anymore. I wouldn't be surprised if "copyright is extended indefinitely if the work is being actively commercially used" or some such

Patents are for 15-20 years.

Which is saner eh! That way people living at the time who are protecting it (copyright and patents are both protections for things otherwise being distributed and which could be copied easily) can benefit from it eventually.

100 years is just rent extraction.