I'm just tired of the signal pollution, and would like to be able to use karma to honestly appraise the worth of my articles and posts, without seeing 80% of my downvotes come in chunks that correspond precisely to how many posts I've made since the last massive downvote spree.
EDIT to add data points:
Spurious downvoting stopped soon after I named a particular individual (not ALL downvoting stopped, but the downvotes I got all seemed on-the-level.)
One block of potentially spurious downvoting occurred approximately one week ago, but then karma patterns returned to expected levels. I consider this block dubious, because it reasonably matches what I'd expect to see if someone noticed several of my posts together and disagreed with all of them, and did not match the usual pattern of starting with the earliest or latest post that I had made and downvoting everything (it downvoted all posts in a few threads, but not in other threads), so I'm just adding for completeness.
Spurious, indiscriminate downvoting started up again approximately half an hour ago on Sunday (12/1/2013), around noon MDT.
Edit: And now on Tuesday, 12/3/2013, at 10 AM, I'm watching my karma go down again... about 30 points so far.
Edit: And now on Saturday, 12/14/2013, at 2 PM, I'm watching my karma go down again... about 15 points so far, at a rate of about 1-2 points per second.
If my memory serves me well, I probably did agree with him on many issues, but anyway, if the accusations are true, I would consider such behavior very harmful for the website (and frankly, also an evidence for some mental problems). I mean, downvoting someone even when they announce a meetup... what the hell?
As I've said elsewhere... I endorse the "downvote what you want less of" metric. It follows that if someone wants me to stop posting here altogether, I endorse them downvoting every one of my posts. (Naturally, I endorse other things more.) So I'm reluctant to endorse automatic mechanisms to prevent such behavior.
That said, I would be OK with a lifetime sitewide cap to how many downvotes user A can issue to user B. I'd prefer making voting behavior public, but that has all kinds of other effects.
As for whether it's harmful to the site or not... I'd say it depends a lot on the user being downvoted.