The mod banning these users is the same mod who made the posts they downvoted. This is mod abuse, turning the downvote button into an auto-self-ban button.
The message is “If you disagree with me, you will be banned”
Monitoring and banning users for using lemmy as intended to signal boost your opinion should be grounds to have all mod privileges removed. This behaviour undermines the integrity of the server and the wider fediverse.
You’re actively arguing for vote manipulation on the part of moderators.
I think its justified for community moderators to ban an account that never interacts on their community, and downvotes everything. I think it’s not justified for community moderators to ban an account just for a single downvote on any thread.
I think if there’s a serious problem, people can either make their own version of the community on another instance (a perk of the fediverse) and lead people away from the problem community to there, or pressure the instance owner in which the community is based - to remove them (another perk of accountability that doesn’t exist in the same way on Reddit).