It's the same with software. For example, recently the well-respected coder Zed Shaw explained in detail why he turned to the GNU GPL to prevent free riders. Note that this was not a question of a headstrong creator imposing an arbitrary condition on the use of his software, but a matter of preserving the very dynamics of sharing that made sustained creation possible in the first place.
Contributing to projects that use more permissive licences than the GNU GPL means that it is likely that many will not contribute because of their distaste for free riders.
That doesn't mean that everyone will refuse to contribute on these terms, just that projects using the Apache licence, say, are self-selecting for those who are not so worried by this aspect. But it does undermine the argument advanced by some that more people are likely to join projects with more liberal licences. Yes, people from non-free projects are more likely to join, but it is also likely that those more committed to the idea of sharing on a fair and equal basis will not join.
So whether you view things from a strictly ethical viewpoint, or simply from a pragmatic one, it seems to me that the GNU GPL emerges as the best solution. Ethically, only the GPL, with its emphasis on propagating freedom for the user, strives to make the world a better place, rather than one that has more cool stuff made out of bits, some of which may reduce users' freedom. In terms of efficiency, the GNU GPL ensures that there are no free riders, and so can tap into the powerful human instinct to cooperate on a share and share-alike basis.
I don't think the recent flurry of posts and comments calling into question value of the GNU GPL is a bad thing, or even a sign that the GNU GPL is on the way out: according to Black Duck, the cumulative share of GNU licences is around eight times greater than the next most popular (the Artistic Licence).
Even taking these figures with a generous pinch of salt, as I do, they are indicative of a world dominated by GNU licences, whatever the exact shares.
And while it's true that the rise of cloud computing poses challenges for the world of free software, those challenges are not really about licensing: they're about the dominance of a few very large companies and their increasing power over us.
Even if they gave back all the changes they made to the free software they used, that would not solve larger problems of freedom, which have to do with access to data, privacy etc. This means that the current GNU GPL – even the AGPL – needs extending to include those aspects. Judging by some comments he made at the recent Gran Canaria Desktop Summit, I'm not sure whether Richard Stallman is fully aware of the seriousness of this problem yet, so maybe there's some work that's needed there.
And to those that say companies like Google and Facebook will simply carry on as they do now, using free software, and giving back in only a limited fashion, I'd say that it's early days. I use Google because there is no alternative, just as I used Windows before I made the move to GNU/Linux. Once there is are alternatives that respect me in the way free software respects me, I shall move, and I suspect others will too.
Those companies are bound to emerge for the same reason discussed above: eventually, the people writing the code that underpins most Web 2.0 startups will take action against free riders, and companies that refuse to give back in the fullest sense – not just the odd scrap of code here and there – will find themselves unable to tap into the ever-increasing store of free software that they've always depended on.
They'll survive, of course, but they'll survive as Microsoft does: fighting a losing battle against the laws of software production, which mean that there always comes a point where the software is simply too complex to be produced by traditional, top-down management processes burdened with the intellectual and emotional baggage of years of pre-existing code.
Empires rise and fall; software behemoths come and go; human nature remains the same. That is why the GNU GPL, which seeks to protect and promote one key aspect of our humanity – sharing - will always matter.