There's a concept of "contributory" infringement: while you're not personally infringing the copyright, you know about the infringement and you're helping it, e

There's a concept of "contributory" infringement: while you're not personally infringing the copyright, you know about the infringement and you're helping it, encouraging it, and so on. This is what the studios sued Sony under for the Betamax. Of course, they lost, and that precedent is helpful for Yuzu, though not a total slam dunk: what they wrote on their website in terms of marketing and instructions and so on could matter here, what the devs wrote to each other or publicly that might reveal their knowledge and encouragement of infringement could matter, etc. More significant is that the Betamax case is from the 80s and precedes the DMCA. The DMCA's anti-circumvention provisions are broad and have been interpreted broadly. The result is that the decryption is a problem all on its own, regardless of things like fair use that were a major factor in Sony's victory. It's worth noting that Nintendo's first three claims are DMCA section 1201 anti-circumvention claims, with the other claims of personal infringement by the developers and contributory infringement (where the part you quoted is from) being kind of tacked on at the end.