I believe that the policies relating to YouTube conflate two distinct issues: posting YouTube content on the Forum versus posting information about downloading YouTube content on the Forum.
I have no problem with banning content taken from YouTube on the forum, and I doubt if anyone else has a problem with it either. I've seen a lot of posts on the Forum, though hardly a significant fraction of the total, and in none of them was there any content taken from YouTube.
The program youtube-dl is available from a number of respectable sources such as webupd8 and github.com. Even if webupd8 is in some sense violating YouTube's rules (and I don't think it is), it isn't a party to those rules. I don't think it takes a lawyer to understand the issue of posting information about downloading YouTube videos on the forum, since nothing in YouTube's policy talks about that.
At worst there might be a legal issue about posting information on how to circumvent YouTube's restrictions, but even that is very uncertain -- and such circumvention, though conceivably illegal, would still not be a violation of YouTube's restrictions. And for the Ubuntu Forum to reference the availability of a package on webupd8 without actually providing the package would be at worst a second-order or third-order violation. It reminds me of the old T-shirts displaying the DECSS code.
I hope this post is not in itself a violation of Ubuntu Forum policies. It shouldn't be.