Copyfree is not the same as copyleft.
The Free Software Foundation has this to say about copyleft:
Copyleft is a general method for making a program or other work free, and requiring all modified and extended versions of the program to be free as well.
The simplest way to make a program free software is to put it in the public domain, uncopyrighted. This allows people to share the program and their improvements, if they are so minded. But it also allows uncooperative people to convert the program into proprietary software. They can make changes, many or few, and distribute the result as a proprietary product. People who receive the program in that modified form do not have the freedom that the original author gave them; the middleman has stripped it away.
The key to understanding copyleft is in license heritability and the availability of copyrighted material. (more text forthcoming)