Making every American adult a homeowner was always imprudent and impractical; now that's obvious. Four years ago, President Bush declared: "The more people who own their home, the better off America is." And as his administration proposed federal guarantees for mortgages without requiring down payments, then-Federal Housing Commissioner John Weicher told me in 2004: "We will have some defaults, but nearly all those families will remain homeowners." The challenge is to tighten consumer-protection rules to discourage abuse and fraud, but not so much that only the better-off half of Americans can buy homes. One option is to require lenders to...