Let me open saying I don't care about Mario Kart 8 auto-steering. You can disable it and play the usual way if so you wish, and you' ll probably do.

I also don't care it's turned on by default. People who care about it will find the menu eventually, and people who would enjoy it are not the kind of people who would dig menus for that kind of option.

If anything, I found it smart of Nintendo do put such an option. This allow people of different skills (for example, a family or a large group of friends) to play together. The veterans will breeze but someone who never touched the game can finish the course without hitting every guard rail on the way.