I wrote this in another context and thought it might be useful to put here for general consumption. The motivating question was about statements people may add to their CC-BY-SA works saying that they deny permission for their work to be used for training AI.
I strongly recommend against using the AI line for a couple of reasons. One is that it seems to contradict the very explicit terms of the CC-BY-SA.
No downstream restrictions. You may not offer or impose any additional or different terms or conditions on, or apply any Effective Technological Measures to, the Licensed Material if doing so restricts exercise of the Licensed Rights by any recipient of the Licensed Material.
This in theory creates legal liability for you because you are not complying with the license that let you create derivative works. No current owner of Atlas Games is going to go after you for this, if you're only using the Ars Magica material that we did in fact put under the license, of course. But perhaps my heirs and assigns will be rapid pro-AI zealots.
A second and more important reason is the downstream liability. You're abandoning the super clear CC-BY-SA for something hybrid that has an unknown impact across jurisdictions. Is it enforceable? Is it enforceable in some places but not others? If I as a creator respect it in my work that is derivative of yours, what about people who derive from my work? You create a new spell; I put it in my adventure; someone else uses my adventure for training an AI. Did I have a legal obligation to carry forward your anti-AI clause, on the chance that it might be valid in some or all jurisdictions? If I don't, and you take issue with the person who trained AI with my adventure that used your spell, am I going to get caught in the middle, either because you sue me for not preserving your additional condition; or because you sue the third party, and they in turn pull me in saying it was my fault for not notifying them of an additional condition? If I do include the same anti-training restriction, am I then no longer complying with the CC-BY-SA and thus potentially infringing the preceding work(s)? And regardless of how it plays out in decisions in the end, who can afford all of that legal nonsense?
The reasonable course of action is for third party creators to actively AVOID any material that asserts any additional conditions on their CC-BY-SA. It could be "no AI training," it could be "no commercial use," it could be "no using this to glorify white supremacy or with Nazi symbols" or "no use of this in works that contain visual depictions of the Prophet Muhammed" or "no use of this in works that include nudity or sexual depravity." All of those might be perfectly legal restrictions in various jurisdictions -- but once you attach them to a CC-BY-SA work, you've created a legal mess for anyone who wants to take advantage of the Share-Alike, which honestly is against the whole purpose of share-alike.
And this is a problem to me because it essentially creates a series of creative cul-de-sacs, branches of what was meant to be a shared open development that become enclaves that have to be kept separate from the rest with their own rules. I don't like that because of its impact on the community, but I also don't like it because it could be used intentionally as a way to wall off a separate garden, the "Disneyfication" of what had been the commons.
Having said that, I am not a lawyer, and the further anyone goes from the CC-BY-SA 4.0 license itself, the more they really should hire their own intellectual property attorney for legal advice specific to their unique situation and needs.
