The problem with "the GPL is freer than the BSD license" is that it's the wrong question to ask, because the perspective is too narrow. What matters most IMHO is which license will lead to the largest and most viable ecosystem of free software. If you take this perspective of a whole ecosystem instead of the license of a single project, a lot of complex dynamics and unintended consequences need to be considered, and it may make more sense to investigate empirically instead of armchair arguing.