Public domain is something different from an emulation of "there is no copyright":
You can take public domain material to build some program binary:
- In the current legal system, you can enforce restrictions on the usage of this binary, and can forbid redistribution, reverse-engineering, ...
- In a "no copyright world", you cannot enforce such restrictions.
IAAL and am pretty familiar with U.S. copyright law, and am curious where support for this proposition in the law is found. Can you provide sources, please?
1. Take some CC0/public domain source code.
2. Build a binary out of it and sell licenses for your software.
Case study: SQLite's source code is public domain. On the other hand, it is embedded in many commercial software products that are sold - and you are not allowed to reverse-engineer the software or redistribute binaries of it. This would be possible/allowed in a no-copyright world.