I'm wondering if there's a way to put a lock-out on this feature to prevent temptation from less experienced gamers you might happen to be playing with? Like, imagine a friend or sibling that you want to play with. You're already going easy on them and helping them along the way, but the idea is to help them improve (you know, you get better at games by actually playing them) so that when their skill improves you can move on to harder games and not leave them behind. Sure some parts in NSMB were tricky, but there wasn't anything nail-bitingly hard, and nothing that a little practice won't overcome.
All that I said would be meaningless, however, if this feature is part of a pause menu or something. If they made it a simple button press to swap between manual and auto there's no way to tell when other players swap over to cheater cruise control, unless they flash or make a sound effect or something. If they have to pause to turn on the feature, it at least makes it obvious and allows the other players chance to smack them over the head for being a pansy non-player.