Notwithstanding the provisions of sections 106 and 106A, the fair use of a copyrighted work, including such use by reproduction in copies or phonorecords or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright. In determining whether the use made of a work in any particular case is a fair use the factors to be considered shall include— ...
-- 17 U.S. Code § 107 - Limitations on exclusive rights: Fair use
How can you prove that youtube dl is used specifically for, say, classroom purposes? Can you prove it? Probably not.
Is circumventing a copyright mechanism an educational or journalistic purpose? In a testsuite? ...
Even when siding with you, you would need a court case to evaluate whether fair use applies or not.
Again, as I said, unnecessary attack surface. I don't care whether you or I am right or wrong. Nobody of us can be right unless a court case has been made.
Fair Use is a circumstancial definition in the law. It is not clearly defined and needs a court case in order to apply.
Therefore I still think that the assumption of Fair Use to apply is wrong. However, the assumption of copyright to apply on the other hand is correct.
But, referring to whether fair use exists or not, I agree with you that technically it exists.
But as the rest of the very same law criminalizes by default, you can still not refer to fair use if you do not have the required-by-law evidence at hand for it to apply.
I think that fair use is almost always nearly impossible to prove, that's why I wrote my statement like this. And I agree that it was worded badly.
Copyright is certainly easier to interpret than fair use, but both rely on courts.
If I claim you violated my copyright and you disagree, it will be determined in court. If I claim you violated my copyright and you claim it's fair use, and I disagree, it will be determined in court.
Fair use is not a “right” (as in a well defined thing you can do freely) but rather a “defense” if someone claims a copyright violation. It’s defined in terms that need to be evaluated by a judge case by case (e.g., if there is an economical damage).
Actually, in Lenz v. Universal, Fair Use is more than an affirmative defence:
we hold — for the purposes of the DMCA — fair use is uniquely situated in copyright law so as to be treated differently than traditional affirmative defenses. We conclude that because 17 U.S.C. § 107 created a type of non-infringing use, fair use is "authorized by the law" and a copyright holder must consider the existence of fair use before sending a takedown notification under § 512(c).
As another comment pointed out, youtube-fl is not _circumventing_ the mechanism, it is merely using it as intended by its creators. It does exactly what a web browser must do to play the said videos. Just like a browser is allowed to do the same thing to get the right video, put it right there in plain data on your computer and play it - no proprietary DRM ever steps in the process! - , youtube-dl follows the same steps. So youtube-dl is no different from a browser that also has a "download to your computer" button - every other behavior is the same.
"Educational" isn't a blanket license to copy. Otherwise there would be no textbook publishers, or companies that make films for classroom use.
(I have a friend who makes a living as a choral composer. Churches, he finds, are the biggest thieves! They believe they don't have to pay for music because they're a Church.)
-- 17 U.S. Code § 107 - Limitations on exclusive rights: Fair use
https://www.law.cornell.edu/uscode/text/17/107