What Threat Do For-profit Universities Pose?

With the growth of for-profit colleges and universities has come growing criticism regarding their recruitment practices, their quality of education, as well as their graduation rates, to name a few.  Many traditional universities have come to see for-profits as a threat to their enrollments, and they have come under heavy scrutiny by higher education regulators and the federal government.  Critics have gathered additional ammunition with the release of a 2011 U.S. Government Accountability Office (GAO) report, which casts for-profit universities in a negative light.  Recent comments by Senator Tom Harkin have indicated that for-profits face a contentious battle and closer examination.
This topic has created a lot of heated discussions from those on both sides of the issue.  Are for-profit colleges and universities truly a threat to traditional universities or do they, as they vehemently argue, provide opportunity to a portion of the population that is largely ignored by traditional universities?
There is no denying the growth that for-profit universities have enjoyed.  According to the Almanac for Higher Education 2011, the numbers are remarkable as seen in this chart.
The University of Phoenix and Kaplan Higher Education Schools are two of the for-profit universities with the highest enrollment.  Despite the criticism levied from traditional brick-and-mortar schools, for-profits argue that they serve a segment of the population that is largely ignored by non-profits.  These groups include, older students, stay-at-home parents, veterans, and those employed full time that just are not looking for the college experience that campus life may offer younger enrollees.  For-profit universities appeal to the student that would normally be denied admittance to a traditional university since for-profit admission’s policy is less restrictive.
The debate rages, but the reality that for-profits face, includes greater inquiry from legislators that can’t be denied.  For-profit universities have a long history in our country, and have filled a training need for much of a population seeking higher education since the 1600’s.  Their future status, however, is under attack and their sustainability may require changes in their methods.  The question remains: Are for-profit universities truly a threat to higher education?