1) "You mentioned teaching as a place where you can't possibly get volunteers to actually work." Uh... no, I didn't.
2) "There are tons and tons and tons of people who love teaching." True, but from what I've heard, teaching in a public grade school has very little to do with teaching. It's more about counseling and disciplining somebody else's kids.
3) Adjunct professors teach at universities. Teaching higher education is a lot different than teaching grade school. And a lot of those professors teach because they need money for research, and in order to get support and resources from the university, they are required to teach.
4) Who is going to volunteer to be a cashier? Or a garbage collector? Or deliver mail? I can't imagine anyone volunteering to wait tables. And in order for a restaurant to pay people enough to wait tables, they'd have to charge exorbitant amounts for the food. Your free $30K won't last long if a hamburger costs $50.
The situation you describe sounds like one where everyone just does what they please and robots do what pleases everyone to not do. And if you think that sounds like a good scenario, then you clearly haven't been exposed to enough sci-fi, my friend. We need to put the fear of robots in you!