If I spent my time on a term like that I'd probably go for copyleft too.
Why?
Probably because Stallman is not attractive enough, or some similarly idiotic reason.
because GPL tries to reinvent the definition of "free" (I recommend consulting a dictionary, and than reading what GPL considers free/freedom, you are in for a mean suprise).
Personally I avoid it because it's incompatible with GPLv2 only licences, which would prevent certain projects mixing code.
Because viral licenses get real terrible when you want to get features from two that are mutually incompatible. When two projects have different ideas on imposing "freedom" on users, it makes it harder to cooperate and make a better end product for the users. As such, I much prefer free as in free licenses like BSD over restrictive licenses like the GPL.