There are three players in the student loan game: lender, servicer, and guarantor. The lender is pretty much what it sounds like. The servicer is the agency that handles the repayment process (and any deferment or forbearance) as long as the loan is not in default. The guarantor is where the loan is transferred if it goes into default.
The guarantor will add collection fees of up to 20% of the defaulted balance, and can pursue those collection methods I mentioned earlier. They can also hire an outside agency to do collections. Their main job is to get loans out of default, either by rehabilitating the loan (a process whereby a borrower makes 12 on time, consecutive payments, and the loan is kicked out of default status), or directing the borrower to consolidate.
Navient falls under the category of lender or servicer (or both), depending on the specific loan. Their interest is in stringing out the payments as long as possible, and wring out as much money from the borrower as they can, which is why they got into trouble recently for directing borrowers to deferment and forbearance options rather than lower payment plans.
If that sounds like a lot of people interested in putting 18 year olds in debt, it is. I worked in this industry for a couple years on the consolidation front, and heard a lot of sad tales.
These articles from The Consumerist give you a better idea what the outrage is about:
https://consumerist.com/2017/04/03/navient-claims-its-under-...
https://consumerist.com/2017/01/18/student-loan-giant-navien...
I think the first covers the "moral outrage" a bit more than the second when it mentions how Navient's public statements are all to the effect of "we're here to help you," while their actions all point the other way. The second is just some straight up shady shit they've been doing.