Medusa broke her vow to Athena and was punished for it

The argument

The case for treating Medusa as a villain rather than a victim rests on the nature of what she did: she made a binding commitment, broke it by choice, and was punished for the breach. The commitment came first. Medusa made a vow to the virgin goddess Athena that for as long as she served the goddess she too would remain a virgin. In Greek mythology, making a vow or a promise to someone is binding, and it is especially binding when the vow is made to one of the gods. A promise of that kind is not a private resolution that can be revised, and breaking it is an act against the god rather than a change of mind. The breach followed. When Medusa willingly entered into an affair with Poseidon, god of the sea, she broke that vow to Athena. The word carrying the weight is willingly. Since her relationship with Poseidon was a choice, the argument holds it is just as likely that everything they did together was mutual, and that Medusa did not do anything she did not feel compelled to do. On this reading she is not someone to whom something was done, but someone who acted, and who can therefore be held responsible for acting. The aggravation came last. The affair became far more offensive to the goddess when the two of them decided to conduct it in Athena's own temple: the breach of the vow was compounded by committing it in the one place dedicated to the goddess it wronged. What followed was a response to that disrespect. Athena lashed out and turned Medusa into a gorgon. Because Medusa broke her vow to Athena, and did so by her own choice and in Athena's temple, she was punished for it — and on this account she is a villain.

Premises

Counter-arguments

One can make the case, however, that Medusa did not enter into her relationship with Poseidon willingly. Another version of the story suggests that Poseidon used Medusa to humiliate Athena. To do this, the sea god violated Medusa in Athena's temple. This telling of the myth also does well to note that Medusa reached out to Athena, both for guidance and forgiveness. What this version shows is that Medusa did not willingly break her vow to Athena, which only further attests to the idea that her relationship with Poseidon was not consensual.

Rejecting the premises

[Rejecting P1] The vow appears in later retellings rather than in the earliest sources, where Medusa is one of three Gorgon sisters and no priesthood or promise is mentioned, so the premise begins from a version of the myth that is itself a reconstruction. [Rejecting P2] The claim that the encounter was willing is the argument's crux and it is unsupported. Ovid's account, the fullest ancient source for the episode, describes Poseidon violating Medusa in the temple — so calling it a mutual affair contradicts the source most often cited for it, and nothing is offered in its place. [Rejecting P3] Even on the argument's own telling, the punishment fell on Medusa alone while the god went untouched, which describes an act of divine anger rather than a wrong she committed — and someone punished disproportionately is not thereby a villain.