[JohnFen]

> It allows the copyright holder to monopolize the copying and public performance of the work. That’s it.

Yes, we aren't disagreeing here.

> It’s not a copyright violation for me to take your copyrighted painting and draw on it with crayons or hang it on a wall labeled “World’s Worst Painters.

Exactly correct. I wasn't talking about purely private use. Copyright is about distribution of the results. If you do something with a work and never distribute the results, copyright doesn't enter into it (ignoring the complications of the absurd anti-circumvention clause of the DMCA, anyway).