The most controversial GSE reform proposal is the notion of limiting the investment portfolios of Fannie Mae and Freddie Mac. But doing so would be a “serious mistake,” according to Freddie Chairman and CEO Richard Syron. In comments at the recent annual convention of the National Association of Home Builders, Syron addressed what he characterized as “the heart of the matter” of GSE reform, and provided four reasons why arbitrarily cutting back Freddie’s retained portfolio…