Nobody gave a shit when Sony & Activision did it.

That's a total lie. The scorehero forums were in a massive uproar when Activision started taking down guitar hero videos, so much so that we used to have all kinds of tricks circumventing the content ID matching system that's now as widespread as ever.

Its nintendo, nothing else to say.

Yes, the fact that you can play older Mario titles with emulators instead of buying them as VC-titles needs more advertisement.

I was saying it in regards of all Nintendo titles that usually get hammered down in Youtube. But even if I were talking about Mario Maker, if someone saw videos of old hacks and heard that with MM you could do them easily too, it would be equally good, no matter they weren't talking about Mario Maker itself.

Emulating a game you legally own isn't illegal.

As long as you yourself ripped them from whatever thing you owned it (a disc, game cartridge, etc.). If you download Super Mario Bros. 3 on the internet, and play it in an emulator it's still illegal, even if you own the game.

I don't know about that. If you own game that's in two CDs, one of them gets lost/broken, and you have to pirate the game in order to play it again, is that illegal, or should I extract the data from the CD that isn't lost/broken first?

Indeed. So one cannot assume that what he did was illegal. 

I remember people would start changing the pitch of the audio and the guitar strumming would just sound awful (more than usual)