A Problem With Anonymous/Confidential Complaints

Eugene Volokh, in his recent post on confidential and anonymous complaints, appears to have overlooked a problem with such systems: it's very difficult for the accused to mount an effective defense against anonymous accusers.

We had (what I consider) a problem of this sort when I was in college. Students would be accused of X by person Y, but because of administration guarantees of confidentiality the identify of the accuser was withheld from the accused. More importantly, because evidence of behavior X was often intimately linked with the accuser's identity, the accused was often not allowed to see the evidence against em. Needless to say this makes it very difficult to challenge the veracity of the evidence (or the accuser).