Either way, this entire issue is moot. We should wait until such time as JSTOR actually sues Wikipedia, or actually asserts a claim over a specific instance of plain text.
Exactly. If a text is under copyright it can't be on Wikisource. If it's PD, it can be. And we have elaborate mechanisms in place to make sure that part of things works.
As to JSTOR and their contract law, that's between the uploader and JSTOR. If I promise them, in their terms of service, I won't copy the text of a PD document, but then I break my promise and copy it to Wikisource anyway, maybe _I_ did something wrong, but that's between me and JSTOR, and it's up to the courts and whatever Gods may be to sort it all out.
But the guiding principle is-- if it's PD it can go up, it's under copyright it comes down. What private contracts were made between the uploader and other parties-- that's got nothing to do with our project. We can't know what private side deals have been made, nor should we, nor can anyone expect us to.
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Now, if JSTOR, as part of some deal with the foundation, insists the foundation promise to refuse to HOST certain public domain texts, no matter who contributes them, then that WOULD be a dealbreaker I think. But they haven't asked, so we'll cross that bridge in the unlikely event that we come to it.
Alec