For most Americans, their home is the largest and most important investment they will ever make. Ensuring that they have the right kind of mortgage is critical to their financial well-being and — as we’ve seen recently — critical to our entire economy. That means we have to solve the Fannie Mae and Freddie Mac problem and eventually figure out the proper role of the federal government in supporting a secondary market for home mortgages. Doing that right is one of the most important issues facing Congress and the Obama administration. Some people ask, Why do we even need a secondary market for home mortgages? Why don’t we just go back to the good old days before those markets existed and require banks to hang on to all the mortgages they create? Let me tell you why.