I stopped using reddit after several such incidents with my raganwald account. After disagreeing with certain users there, suddenly all of my comments and posts would get downmodded in my history.

At first this would cause a karma hit, so I tried a workaround: after my submissions peaked, I would delete them and this would present a smaller surface area for revenge attacks.

This turned out to be a bad idea because it deprived reddit of the history. So I switched to a new tactic: I simply stopped participating in the forums and started submitting things under a nom de plume.

I think that they have changed things so that revenge downmods do not affect karma, but it doesn't matter to me. I stopped one day and asked myself why I was bothering to worry about my reddit karma?

Then I asked why I was bothering with reddit?

Then I closed up the nom de plume and HN is the only such site I visit. And let me tell you, I am a far, far happier man for it :-)