There are alot of flaws in your statement. Voluntary participation isn't a myth when you can choose to go to some other company instead of working for Tesla. I'm sure as an engineer you'd easily get jobs from some other place. Also every job is not 12 hours, most are 9-5 jobs. If a worker doesnt want to work for 12h they can go work for 8 hours, it's personal preference.
Where do you think the materials for the products come from? Who gives Tesla money? Investors, yes, but that is because they trust in Elon Musks ability to make profit, most likely due to reputation/merit and most importantly, SKILL. If you would have a total idiot running Tesla, nobody would invest and the workers wouldn't have anything to produce with, making them contribute nothing to the value of the product. So, you see, while Musk isn't the one who is putting together for example a car, you have to raise the question: who buys all the material for the car?