For each user, PerlMonks tracks a weighted average of the recent votes that they have cast. Each time you cast an up-vote, your weighted average, $vtavg, is set to 0.1 + 0.9*$vtavg. Each time you cast a down-vote, your weighted average is set to -0.1 + 0.9*$vtavg. So somebody who only ever up-votes will quickly have a $vtavg very close to +1 while somebody who only ever down-votes will quickly have a $vtavg very close to -1. If your $vtavg is positive, then each down-vote has $vtavg/4 chance of gaining you 1 XP... If your $vtavg is negative, then each down-vote has $vtavg/3 chance of losing you 1 XP.

Picking up on another post, I think this could be enhanced in two ways:

1. Lower the weight of new votes from 10% to something more like 5%. At 10%, a $vtavg of 1 will go negative after only 7 downvotes. At 5%, it goes negative after 14 downvotes.

2. Lower the threshold for risking losing XP for downvoting from $vtavg < 0 to something more like $vtavg < -0.25.

I don't know that you need to do both of these, either is probably fine. But someone who is very balanced, who frequently downvotes as well as upvotes could easily wind up negative after only a short series of downvotes, which could easily happen in a highly controversial thread, for example.

I think the original proposal stigmatizes downvoting too much. While we want to avoid abuse, we also don't want to stifle inclinations for genuine criticism.