I don't think the work was stolen.
If open AI obtained your work by scraping--I'm sorry. I think it's rude of them to do so. Like showing up at a potluck and not bringing anything. I think they should provide open source models as a way of contributing. Mike's idea of micropayments would also be a nice gesture, but hard to implement.
That said, I do not think stealing is an appropriate term. They didn't steal anything. Nor do I think it is unethical.
I understand this is a somewhat new scenario and new ethical territory, so if you reason about it differently I can understand that.