It's incoherent, like a lot of his recent statements.

They'd owe more than it's worth only if property values go down. In that case, you'd probably be underwater with a 30-year mortgage also, particularly in the early years. Curious whether lenders like this. Does the lower rate of principal repayment increase risk for the lender?

You would still have the equity represented by your down payment plus any appreciation in the value of the property. It's not a great long-term move, but could be a good short-term move.

But the "rent" is deductible. If you sell in, say, 5 years & the profit is greater than the interest you would have earned on the down payment, you can make a profit. Could be a somewhat risky investment.