Look, at the end of the day, the dude is a legendary gamer who put up some incredible high scores back in the 80s and 90s—regardless of what hardware he may or may not have used. Donkey Kong in particular is an insanely tough game that takes an immense amount of skill, dedication and practice to master. And Mitchell undeniably put in that work. You don't get to nearly 1 million points by being a scrub.
Controversy aside, Mitchell helped put classic gaming on the map and bring mainstream attention to the competitive Donkey Kong scene. For that, dude deserves at least some respect. And while the evidence against him seems pretty damning, he's never admitted to cheating and deserves the benefit of the doubt until proven otherwise.
So while I don't condone cheating and think using an emulator would be lame as hell, I also don't think that should entirely negate Mitchell's accomplishments in gaming. Hate the game, not the player, ya know? But hey, I'm just trying to look at it from all angles here. You can make up your own mind about the guy.