When someone has obviously put effort into contributing to the conversation, it's rude to downvote them to negative scores. Most recently, there some major offenders here:
http://news.ycombinator.com/item?id=720779
and here:
http://news.ycombinator.com/item?id=720215
and here:
http://news.ycombinator.com/item?id=720569
Someone disagrees with you and does the initial downvoting, then groupthink kicks in and your score hits the floor.
It's a simple fact of life in social media sites (it occurs on many sites with differing communities), this is why PG put in the -8 limit, to combat the detrimental effect of this kind of groupthink.
Honestly, deal with it, it's just online Karma, a simple numerical value... what effect does it really have after you've unlocked various features on HN.