I am the director of Tlön, an organization that translates content related to effective altruism, existential risk, and global priorities research into various languages.
Every post, comment, or Wiki edit I authored is hereby licensed under a Creative Commons Attribution 4.0 International License.
Alternatively, you could make the downvote button reduce votes by one if the vote count is positive, and vice versa. For example, after casting a +9 on a comment by strongly upvoting it, the user can reduce the vote strength to +7 by pressing the downvote button twice.