Has anyone yet mentioned or reported that for the last couple days, the "karma for last 30 days" is showing zero for everyone? And that we no longer can see the top contributors for the last 30 days either?
Do we have an explanation or estimation for a bugfix on this?
In addition to what others said, people will be discouraged from explaining downvotes. (Or maybe encouraged to explain even minor downvotes.) Once a comment is at -3 without a (good) explanation in a reply to it, people will not want to pay a penalty to explain to a potentially well meaning poster what was wrong with their comment. Instead they will be incentivized to further downvote it without explanation.
Not all comments deserving -3 karma are trolls, some are merely stupid / insensitive / wrong / unoriginal.
This change will make people think: is this comment a troll? If it is, downvote it to -3 or beyond; if not, don't downvote below -2. If that's desirable behavior, and we come to agree about it, and -3 is the right level for it, then we will have many comments at -2 that previously would have been downvoted further, because people will not want to tell others "you're trolling" unless they really think so.
(And then people would probably want comments hidden at -2, not -3: the karma level of bad, though not quite trolling, comments.)
Not all comments receiving -3 karma are trolls either.