Two suggestions to mitigate abusive downvoting
19373
Should we have a policy about "too much downvoting"?
38709
How to prevent negative comments/downvoted being deleted by re-posting answers
51696
Select from list of reasons when performing downvotes
54233
The answer to tactical downvoting problem?
112477
How to deal with downvoting sock puppets?
12870
Would any other people want to remove downvoting
39421
A guide to moderating comments
145834
Can you appeal against a downvote on Stack Exchange sites?
22027
What can I do if I'm the victim of serial downvoting?
54812
Comment upvote, undo, and then re-upvote: why not?
71881
Questions with many upvotes should not be closable
55618
Option to be notified when a post I downvoted is edited
100205
Make it possible to prevent voting on time-limited questions in meta without a historical lock
7089
The "I Get It" Reputation Problem
76517
Split reputation: one for questions and one for answers
57880
Add a note about downvoting on Meta
128814
So annoyed with no-comment, vindictive downvoting