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.
People with a very high sense of responsability towards others generally avoid taking on responsabilities were their own mistakes might cause problems to others - for them such positions are a “weight on their shoulders”.
People who seek power, on the other hand, generally tend to do it because of perceived social prestige or what they can do with that power. The less they feel that sense of responsabiliy to offset such attractive elements in having power the more they want power.
This is a well known phenomenon: for example there are tons of sayings about how (political) power should be given to those who do not want it not those who want it, and there’s actually a Harvard Business Review article from over a decade ago about how they investigated this in companies and found that companies where the CEO unexpectedly got the position rather than seek it, in average outperformed the rest of their industry.