By the definition of free (http://dictionary.reference.com/browse/free)
“19. frank and open; unconstrained, unceremonious, or familiar.”
“23. that may be used by or is open to all”
“Free” can clearly what is commonly understood by it.
None of those definitions of “free” support Stallman’s position of “giving derivatives of use back”. They don’t seem to support having to give anything back, else it wouldn’t be “free”.
That's the perfect definition. The catch in the GPL, MPL and CDDL is that the original work must remain free to be used by and open to all. In contrast, BSD works can be made closed, and thus no longer free.