|laziness, impatience, and hubris|
I share roboticus' methodology in this post they wrote for upvoting, but with one further addition... I'll usually also upvote an OP for showing appreciation to the person who solved the issue, and/or all who provided aid.
As far as downvoting is concerned, I believe I've only used two downvotes in my near three years here on PM. With that said, I'm not against downvoting, as it allows one to create thresholds as to what they want to look at. If something is very offensive, over-the-top derogatory or just plain stupid, I want the option to cast my doubt on that post.
All in all, even if PerlMonks has a few rogue a-holes who just downvote everything, they're likely the type who don't have many votes per day to begin with, and most likely will get bored with it and move on in short order. Also, I'm a *firm* believer that the vast majority of Monks here are positive people who are here for the benefit of the community, so they would rather upvote a good post than downvote a bad one.
If a post is good and one receives negative feedback/votes by a couple douchebags thinking they are going to upset the system, the rest of us who really care will wipe those votes out in a heartbeat.
Down voting stays imho.
Update: To further, I believe I have had but two posts out of the ~200 I've written that ended up in a negative state. That is very constructive criticism, as it shows I'm doing something wrong. In both cases it *was* my mistake, and I believe in each of them I updated the post with such a statement. At work, I WANT both my staff and other departments giving me this critical feedback, as it allows me to not only become more effective at my job, but it also allows me to build my character. It shows I'm willing to communicate and respond to complaints, and that builds stronger teams and morale. I give props to BrowserUK for his approach of commenting on his downvotes. That's a tactic which I am going to forever remember and use.