I didn't realize this was going to be such a controversial take. It's possible you think there's a clear definition because you haven't seen examples of what some industries think is ethical. I'm trying to pick relatable examples but clearly not doing a great job. Again, I tend not to think these things are ethical, but I'm not the ethics police, so the fact that one person thinks it's ethical and one person does not means it must be blurry.

I feel pretty strongly that tracking cookies are evil, but the entire ad-tech industry did not think that was a dark-pattern.

I feel pretty strongly that GDPR "accept all or leave site" dialogs are a dark pattern, but the EU is happy with that implementation.

I would also love to point out that "dark-pattern" is still a blossoming terminology, there's no definitive body of law or ethics that describes what is and isn't a dark pattern.