It is not illegal to emulate a game that you own.

In a lot of place it is illegal to circumvent technical protection measures, which is technically required for almost anything starting from NES era. Making it impossible to "legally" rip your own games (yes, even in places where there IS a tax to allow private copy of content you bought). So the only way you can do that is by downloading it, where there is no "legal" way to distribute it in the first place, so "legally" you can't download it either.

I'm not defending the practice, I'm saying that if you're going the "legal" defense, you're going to have a bad time if it gets attention. Fortunately, suing every single gamer on earth is not an attractive prospect.