Legitimate journals (or groups of journals) might need to institute a throttling mechanism to limit the rate at which individual authors can submit papers. They might also need some kind of reputation tracking system so that reviewers can flag articles as low quality, and then future submissions by the same author will be treated as lower priority. Open access journals can raise author fees.

Punish the people using it, disallow and shame people who are found to use it. The usual stuff when you want people to stop doing things. (Not legally ban the whole population from making use of it even in cases where it's productive.)