I believe that the only sustainable model for software that benefits the humanity has to have a profit motive. Even a delayed one, as in the case of the universities and government grants.
But certainly the free software movement has provided incalculable benefits to humanity, where their authors were not chasing profits. The only reason this is unsustainable _in some cases_ is because we haven't established a good model to support this work yet. There are some attempts with varying success, but even in its current state, I would argue that more good is produced with this model than with one whose primary goal is profit.
