It's also important to remember that emulators exist without ROMs.

All the code that's in an emulator isn't infringing on any Nintendo's IP -- it's re-implementing Nintendo's hardware interface.

That it can be used to make piracy easier is unfortunately, but isn't really the emulator developers' concern, given...

There are substantial, legal, non-infringing uses.

In most legal jurisdictions, thankfully you can't ban something useful just because it might be used to commit a crime.