It seems too good to be true, at least for companies. Customers arrive at for-profit colleges by the million. With them comes billions of dollars of federal student grants and loans, to be poured into corporate coffers. Public subsidies may provide up to 90% of revenue; the government bears the risk of loan defaults. This business model has served firms rather well. Its effect on students and taxpayers is less clear. This summer, however, a brawl over for-profit colleges has exploded at last.