There is no script to reverse the down votes of someone who casts 40 down votes that do not specifically target an individual, just as there is no script to reverse the up votes of someone who casts 40 up votes that do not specifically target an individual.
Well, unless you count the roomba deleting closed questions that have no answers with a positive score (and other criteria) in which case the down votes are kind of reversed in that the target question no longer exists, so the down vote no longer exists either (FWIW, you can cast 2x max votes in a day if all the votes were on questions that were later deleted that day), but thats not what you are thinking.
The following tries to address an earlier revision that could be read with the implication that such a script would be 'protection against generalist serial down voters'.
Downvotes, wherever they may be and however they are cast are an essential part of the system's automatic housekeeping and janitorial cleanup. Trying to slap the wrist of someone who is trying to help these systems receive the proper input is counterproductive to the quality of the site - be it one downvote or thirty.
In particular, downvotes:
- Provide an incentive for users to improve the quality of their questions and answers
- Help separate the good answers from the poor ones
- Help people answering a question decide how much time to spend on a given answer (they are more likely to click through to an unanswered +5 question than an unanswered -5 question)
- Allow 20k users to delete particular answers if they are downvoted enough
- Allow 20k users to speedily delete poor closed questions if they are downvoted enough
- Feed the question ban and prevent people from repeatedly wasting the time of those who answer questions
- Feed the roomba scripts and automatically delete closed questions that lack anything with a positive score
- Trigger automatic low quality review flags
Given that the number of upvotes often is much more than the number of downvotes in general, some people may decide to downvote things to help these systems get the appropriate input they need to work.
There are great numbers of questions out there that are hanging on by a thread that really aren't that great and are adding to the noise in the system as a whole. Quick queries can show closed questions that are at -lots with a single answer that is +1 keeping the roomba from deleting it. There are two ways to delete this question if it isn't adding anything to the site as a whole - either having 3x 10k users cast delete votes on it, or downvote the answer - the outcome is the same.
Should anything be done? No. Downvoting is an essential part of the system. If someone is investing 30 reputation a day in downvoting answers for some reason, they may see that as an investment in the site and its overall quality.
There is as much ethics involved in downvoting poor questions and answers as a gardener spraying herbicide on weeds or pulling them out and tossing them into the compost pile.
Look at the mouseover for downvote answer - "This answer is not useful." As long as you are not targeting a person and down voting them because of them, however you find the questions is immaterial. Be it from a google search, a targeted in site search link, or a data.SE query link. These are all ways to help garden the site.
The site is too big for moderators, or even the active 10kers to do all the cleaning. It is important for people who have less reputation and care about the quality of the content on the site to also help moderate it with the tools they have.