what? no! licenses are how authors are deciding to grant specific permissions on their copyright.

Sure. But that does not contradict what I wrote.

that is like saying because you found a book in a library you have the choice to copy it and sell it.

That is precisely the choice one has. It's a choice one doesn't have when one doesn't know the contents of the book or when they are confronted with closed-source software.

the fact that source is available does not grant any permission besides looking at it.

Yes I agree. "Making the choice" would require making it without the author's permission.
But again, I'm not talking about permissions as I don't really consider them to be nearly as important as availability and ability. One has the ability to modify/use code with the source and without permission one does not have the ability to modify/use code without the source and with permission.

So yes, Libre is nice, but the source-open aspect is always the most important component.