Rather than saying that this is a problem that is temporarily solvable by collective action, I would say that this is a problem which is currently ONLY solvable by collective action. The offenders clearly don't care; the admins clearly aren't going to do anything. It even appears as though the karma assassination has begun, as the user in question's karma has dropped quite a bit in the last few days.
Frankly, having read through a number of the user in question's posts, I'm ok with that, but I don't think it'll work. He seems to get his karma from rationality quote posting, which is a powerful karma generator. His actual comments are IMHO rarely worthy of an upvote and often deserving of a downvote, but he gains much karma from posting other people's brilliance.
Perhaps this is another distortion in the karma system that would be worth looking at. Copy/pasting a rationality quote every few days from last years threads can easily keep your karma at a reasonable level even if the bulk of your other posts are crap or mildly offensive. Perhaps karma from those threads could be configured to not accumulate, or perhaps karma could be 'number of posts upvoted minus number of posts downvoted', instead of a vote total.
Frankly, having read through a number of the user in question's posts, I'm ok with that, but I don't think it'll work. He seems to get his karma from rationality quote posting, which is a powerful karma generator. His actual comments are IMHO rarely worthy of an upvote and often deserving of a downvote, but he gains much karma from posting other people's brilliance.
This is in general problem. There are other users who seem to do this also, but they don't post as frequently so it hasn't created as much of a problem. But in this particular case, it may al...
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.