
I don't even accept the proposition that it's necessarily amoral because formal rules can be (and often are) arbitrary and/or illogical. For example, the moral character of drinking or selling alcohol isn't changed by Prohibition: it can be made legal or illegal by Congress or statute, but taking a swig from the same bottle in your cabinet was not moral the day before and immoral the after Prohibition went into effect. Some laws do concern moral issues but many do not. The only legitimate moral argument against most instances of ghostwriting in academia is that it's unfair competition against other students who write their own papers.
There would be a moral issue if there were a connection between writing assignments and the actual qualifications of students as relates to their intended fields and professions, but not otherwise, and not when those writing assignments are unnecessary in the first place. The vast majority of the opportunity for academic ghostwriting only exists in the first place because colleges waste the time of engineers and nurses (etc) satisfying writing requirements that are useless to them and unnecessary for them. Generally, students who need ghostwriting don't go into fields where their ability to write is important. Engineers need to know engineering and nurses need to know nursing; there's just no reason to force either of them to take History or English Literature courses that they have no interest in and whose material they won't remember a week after their exams anyway. Nobody is harmed by the fact that an engineer or nurse bought a paper on World War II in college. Even when they do their own writing, it's usually nothing more than stringing together the ideas they find in their sources and wouldn't meet the standards of academic writing if their professors cared enough to check beyond just making sure they didn't copy & paste directly from sources. They usually don't check any further than that because they don't care either, precisely because it really doesn't matter.
There would be a legitimate moral issue if engineers or nurses paid someone to take their exams in their majors because that would enable unqualified engineers and nurses to build unstable buildings or dispense the wrong medications. Unless students are going into a field where their actual job emphasizes writing, it's nobody's business (including their academic institutions') that they can't write much more than an informal email, and most students who purchase ghostwriting aren't going into those fields. Otherwise, colleges have no reason to force students to write in the first place because their only concern should be what students learn substantively, and that can be (and is) tested sufficiently on exams; and exams can include essay questions if it really matters that students be able to express their knowledge that way. If they can write well enough to pass an in-class essay-question exam, they can write well enough that it's nobody else's legitimate business whether they choose to work on improving their writing any more than that.
[While I respect both of the posters above, there are also plenty of dummies here who will be tempted to respond with the (very) obvious counterarguments. Please spare me because I can make them better than you can; trust me on that. I just don't believe that the strongest counterargument here prevails on the issues.]