> if X has a public API and Nitter is using it
Public as in being visible to all is not the same as public as in allowing use by all. You appear to be conflating the former definition with the latter. For example, my front door is visible to all, but a person isn't allowed to walk into my house without permission.
The person is allowed to walk to your door. They are not allowed to walk through your door.
It's a totally different thing.
> Public as in being visible to all is not the same as public as in allowing use by all
Where's the limit of that? Can I have port 443 open with a website behind it but sue anyone that accesses it because the fact that it being visible doesn't mean that I allow anyone to access it?