I don't know. The question is whether subsidizing 30Y mortgages (fannie mae/freddie mac/FHA/QE/standard terms enforced by law to enable refinancing, etc.) is the right policy in an open system where it has many major side effects, compared to other ways to adjust housing policy. For reference, Canada has no 30Y fixed mortgages - instead they have 5-10Y fixed terms and distinguish between prepayment for refinancing (exploiting the rate environment) vs. moving (the mortgage can be rolled into the new property). As a policy, this seems less likely to have destabilizing effects than what happens in the US (concentrating volatility by loading up the banks' balance sheets with trillions of refinanced debt at times of low interest rates for folks who happened to have the means and cash flow to refinance at the right time).