> I don't think that a law preventing you from breaking Bob's DRM just because it protects public domain is ridiculous. Public domain just means that nobody owns the rights, it is not an obligation for anyone who owns a copy to make it available to everyone.

That's not what's happening. Bob is making it available to everyone, and then trying to reassert a copyright on something that isn't.

Suppose Bob was the copyright owner, last year, before the work entered the public domain. He never distributed any copy without DRM, so no DRM-free copies exist. This is fine? Section 1201 of the DMCA was created to eliminate the public domain?

You're also missing the point. Stop trying to argue about the specifics of the thing Bob is doing and just choose anything you feel would be illegitimate. Preventing the use of third party toner cartridges, preventing farmers from repairing their tractors, take your pick. That's obviously not what the law was intended to do and it shouldn't be doing that.

But when Bob is using the same DRM as Alice, either you can publish tools to break it or you can't. If you can, the law is pointless. If you can't, the law is wrong.