This may be overthinking things a bit but…
I mod a desert of a sub for my alma mater, and I’m pretty sure the same person downvotes everything I post there. No comments, just a single downvote. As a mod I would love to be able to confirm my suspicions, but as a user, I like my votes to be anonymous.
As a middle ground, perhaps the software itself could auto-mod a bit. If a single user only ever downvotes content from a community, and crosses a certain threshold, they might be soft-banned for some number of days with a note in the mod log to the effect of “negative contribution.” After some amount of time, the ban is automatically lifted. If a community mod notices that the same user keeps getting soft-banned every 30-something days (the soft-ban limit plus some amount of time for it to kick back in), they can decide if they want to ban the user.
Agreed! I’m actually hoping no more people leave Reddit. I like the community here so much better. For sure, there’s some trolls and echo chambers, but it’s mostly a pretty good place.