Saying that one does not need to sign up to a specific view of freedom when using the GPL is a fairly bold statement, a point I also mentioned to James:
The GPL specifies a very aggressive form of freedom: freedom that must never stop. Whereas BSD allows you to take something into a "jail" - as embedding code into a proprietary project -, GPL will have your head for it, and forces you to open up everything it comes into too close contact with. And the proprietary to GPL step is irreversible.
It is exactly this viral form of freedom - the domain of GPL can only grow, never shrink - which I personally think is why the license is so successful.
(Double licensing, or re-licensing if you get every copyright holder to agree, does not change this argument, as it cannot be applied retroactively nor does it detract from the power of the GPL.)
When I heard Team America sing "Freedom is the only choice now", I definitely thought of the GPL ...
All other points about passion and meritocracy etcetera also apply, of course; but that also works for BSD. Maybe Linux had an edge there in the 90s due to the unclear *BSD situation. But the reason why Linux sucks everything in is that the GPL is a black hole. (Luckily.)
But an emergent value? Hardly. It is built into its very core.