You can't really prevent something from being an investment. Which isn't to say I disagree with you, policy should favor direct housing affordability over thin

You can't really prevent something from being an investment. Which isn't to say I disagree with you, policy should favor direct housing affordability over things like price appreciation and subsidizing ownership. I wonder if there's a sensible way to limit how much leverage Fanny and Freddie will back, maybe by shortening the maximum allowed term of mortgages as interest rates fall below some specified point. Not sure you can do that in a way that avoids a cliff though.