Sallie Mae’s successful privatization bid has encouraged some GSE critics, who want Congress to prescribe a similar pill for Fannie Mae and Freddie Mac. But analysts caution that the medicine may not go down as easily for the two mortgage market giants. “Sallie Mae, for the most part, has seemed to benefit from the perceptions of being younger, less dominant and less controversial than its housing-related counterparts,” writes Chuck Gabriel, an analyst at Prudential