When? When do they have a legal and moral obligation to know? Before they agree to anything? One month after? What is the statute of limitations here? You are a parent. What if you make a mistake? You agree to something but you are wrong. It happens to all of us. We looked it up, thought we understood something but made a mistake.
Does that completely remove any responsibility on the other party? Not bloody likely.
Never minding that the idea of "ignorance of the law is no defence" only applies to criminal law. After all, you presuming that everyone has equal access to all information all the time. That's utter and completely ridiculous.
Talk about victim blaming. Holy crap. "Oh well, your honour, the complainant didn't know that what I was doing was entirely illegal, so, I guess that means I'm innocent!" Seriously?
Good grief, companies do this sort of thing all the time. Heck, there are mountains of cases where the company figured that it was cheaper to pay lawyers than to actually fix a known problem. And the worst part is, usually they're right.
The notion that suing WotC because you feel that they have wronged you is somehow unethical is just mind boggling. That's WHY we have civil courts. To determine whether or not wrongdoing was actually done. But you're arguing that the action of suing in the first place is unethical? Good grief.