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.
It's not just you. A few folks have noticed this specific bad behavior.
Mathematically, just correct for it.
Socially, consider that it means that you're posting things that a defector (boo! boo!) disapproves of.
Alternately, one of these days, one of us should run some sort of analysis correlating mass downvoting and other site activity ....
(Also, consider this a measure of the effect that one bored person can have, and the situation that person might be in. As far as I can tell, there's only one mass-downvoter. Consider their lonesome plight!)
I am also getting the same treatment but find it very unlikely that there is only one such person doing this.