The person protected by anonymity and the person harmed by it may both have a reasonable case.

Anonymity protects and it also shields. The same cover that lets someone report abuse or speak safely lets someone else accuse without accountability, and both the protected and the harmed can have genuine claims at the same time. There is no arrangement that gives one without risking the other.

Rather than deciding which side is right in general, look at the particular case: what is the power difference, what would happen to the speaker if they were named, and what recourse does the person described have. Hold both discomforts at once. Positions that feel completely clean on this question are usually only seeing half of it.