I am not a fan of peer review in MOOCs since it makes no sense. There are no peers as would say be the case in submitting to Science or Nature. It is assumed the Editor in each case selects a true peer who has their own track record. Yet in a MOOC setting one gets a total and random collections of people who have generally no experience or knowledge of any depth in the subject. In addition, the cultural difference results in chaos.
But the real issue is what the so called peers see as Plagiarism. Here they walk a very fine line. It appears that the "peers" can assign a paper as plagiarized with no basis for saying so. There is no due process, there is no meeting your accuser. But there is a basis for defamation. Why the companies who allow this have not considered the legal consequences I cannot fathom. You have students from cultures where it is fine to defame others for their own achievements and practicing that randomly online and assuming there will be no consequences. That is unrealistic.
Plagiarism is a bit difficult to prove, unless one finds the source and then demonstrates the exact extraction without referring to the source. We try somewhat diligently herein to be certain at all times to delineate fair use of segments with a reference and where we seek comments. That generally is acceptable. On the other hand accusing someone of plagiarism without basis is de facto defamation.
Why MOOCs allow this practice is beyond me. It may come back to haunt them.In fact it is my opinion that it facilitates a potentially antisocial trend in a class of individuals and the result may be catastrophic.
MOOCs have a long way to go before they work. A small few, again I use Lander's course as the sine qua non example, but there have been frankly none since then. The potential is there but the anonymous discussions create cadres of the strangest types. They may be well worth a study.