It has long been clear that an oily subgroup of for-profit schools was doing very well for themselves by recruiting students who had no real chance of graduating, pocketing their federal financial aid and leaving the students with valueless credentials -- or none at all -- and crippling debt.

A dismaying study released this week by Sen. Tom Harkin, D-Iowa, suggests that this predatory behavior -- which costs taxpayers tens of billions of dollars a year -- may extend well beyond the unscrupulous few to the industry as a whole. The study reveals a disturbing pattern in which companies use misleading tactics to lure poorly informed students into certificate and associate degree programs that average about four times the cost of similar programs in comparable community colleges.

According to the study, taxpayers poured about $32 billion into for-profit colleges in the most recent year -- much of it spent on marketing or pocketed as profit.

Meanwhile, 96 percent of their students were forced to take out loans, as opposed to about 13 percent in community colleges and 48 percent in four-year public colleges. A majority leave without degrees. And while the for-profit sector accounts for only about 13 percent of enrollment nationally, it accounts for nearly half the loan defaults.

This is a politically charged issue, with the Democrats generally favoring tougher regulation and the Republicans favoring the for-profits as a useful alternative to overcrowded community colleges and important sources of vocational education. The good ones may be both. But too many of them look like nothing more than profit centers.