The copyright holders can be harmed by actions other than direct copyright infringement. In particular, the law recognizes DRM circumvention as a harm. Other commenters had already covered this aspect before I made my comment, so I'm unsure why you expect me to cover it again.
Well, it's very similar to many other real situations like common household doors. They provide a weak level of protection and we add laws that criminalize getting unauthorized entry.
I'm sometimes baffled that people miss that point when it comes to internet security. The biggest real difference is the global nature of the internet and thus problems with jurisdiction, which obviously doesn't apply if both sides reside in the same jurisdiction.
This particular protection mechanism is bypassed by all browsers when they access the content. Are browsers infringing too?
Clearly what is most important is the intent. In this case, it is very clearly RIAA's intent to make the aforementioned videos obtainable publicly via the use of HTTP agents. Browsers are HTTP agents. youtube-dl is an HTTP agent. Either they are all infringing or they are all not infringing.
On the other hand, it is clearly the intent of my door and lock to keep people out.
You're absolutely right. From my non-lawyer understanding that's why the youtube-dl dmca mainly rests on youtube-dl showing illicit use within their code (download of copyright protected material) and not that the tool is theoretically capable. But it's indeed a slippery road.
There are other examples in the real world tho, where the distribution/creation of the tool is already illegal (e.g. certain weapons or explosives), because only reacting after damage is done is infeasible.
Not necessarily. Public domain and fair use don't require distribution to
occur. Ex: Photos taken in the 1890s are public domain, and you may know that they exist (having seen a print in a no-photography-allowed museum), but the owner of the only copy of the photo is under no obligation to distribute them.
Lets tackle explosives:
Where public interest exists for legitimate use, they are allowed: mining, fireworks, and hobby rockets. And there is real risk of grevious bodilly harm associated, even if used properly - we are not even considering terrorism.
There is massive legitimate use for downloading videos, yet the alleged harm is purely monetary.
