While opponents of homeownership claim it's "the American nightmare," self-made millionaire David Bach is doubling down on his faith in real estate.He thinks that not prioritizing homeownership is "the single biggest mistake millennials are making."Buying a home is "an escalator to wealth," he tells CNBC.Young adults in particular aren't hopping on this escalator, and it's a costly mistake, Bach warns: "If millennials don't buy a home, their chances of actually having any wealth in this country are little to none. The average homeowner to this day is 38 times wealthier than a renter."The self-made millionaire is quick to say that the smartest investments he's ever made have been the three homes he's purchased. He tells CNBC: "I first bought a home in San Francisco. It skyrocketed in price. I moved to New York and bought another home. It skyrocketed in price. My net worth has gone up millions and millions of dollars, simply because I've lived."