I am entirely sympathetic with your concerns. It is indeed an outrage that we are being virtually blackmailed into fighting these bogus claims by would-be inheritors of the public domain; either that, or face extinction. Unfortunately, that's the way the game works; that's the way the world is. As such, permit me to respond to some of your apprehensions:
The idea of a Public Domain Foundation (PDF) is precisely to answer the question, "Who will pay for protecting our rightful heritage?" Yes, it costs a lot of money to mount a good defense, a heck of a lot of money, effort and time. However, if you noticed, Feldmahler and others have indicated that university legal staffs and others have come forward to offer (some of it, pro-bono) their assistance in this matter. If we use those offers on a one-shot, one-time effort to save just the IMSLP site, then the resource will simply be used and lost. Other attacks by other challengers will need to mount whole new efforts each time, starting from scratch. That will really be a very doubtful proposition. If, however, a permanent foundation is created to manage these matters, secure willing counsel, raise money and perform other tasks over a range of public domain sites and issues, then it may be possible to present far more effective challenge to encroachment and long-term protection across the spectrum of public domain issues.
We cannot afford such structures by ourselves. But, taken together, under a single umbrella organzation, the PDF itself may be able to raise such funds, obtain both paid and volunteer resources, gather expertise, cast a watchful eye and stand as our advocate in the battle to keep the public domain both open and free. That's what such organizations do best and I would leave it to competent attorneys and other experts in organization to figure out how that might be done. It remains our best chance; for this effort and for future efforts.
As you can see, from things like Microsoft's effort to buy out the right to present images of the world's great art to RIAA's attacks on music downloaders, "jumping the obstacles" or "going around" them, is at best a very temporary measure. The forces that would bully this site into non-existence will come back again and again unless we push back on a level playing field and on equal terms. That's just the way it works and fairness or even right and justice rarely have anything to do with the matter. As you infer, what is "right" is often defined by those with the power (ie. money) to assert definitions that advance their own agenda.
So, that is why I suggest that Feldmahler and others involved at least press the suggestion that we need to create a PDF or something like it to manage these matters in a united and concerted way. EFF did it for privacy and public rights for internet users. Why shouldn't a PDF do it for the preservation and distribution of our own cultural artifacts?
Something to think about. My best - Red
In a world where so many have abdicated
all sense of sanity and reality, it is to the arts
that we must depend upon its safe-keeping until their return.