I think it's misleading to conclude that we must either fight for it with legal methods like viral copyright licenses or just accept that corporations will make a lot of money without paying. There are obvious reasons for corporations to tithe money to open source projects. And, from a risk management standpoint, it is increasingly beneficial for them to do so as a security measure to make sure that their important dependencies continue being developed.
On the other hand, the necessary increases in open source donations do not seem to have happened perfectly in a vacuum. I would first suggest social stigma as one factor to the solution, but corporations only seem to respond to that when the advocacy comes from within (see Google walking back its technical support of China's censorship). Failing that, legal remedies might work, but I'm eternally skeptical about the efficacy of enforcement and I'm sure new, completely free alternatives would turn up to replace any of our current open source dependencies that adopted a mandatory payment model. If the way the market moves is toward completely free, then the market must adapt to keep itself sustainable, even if that means the market needs to read an economics text more complicated than "Supply and Demand" or "Obey the invisible hand."
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