First off, as of early last year, I noted [1] that there is in fact quantitative evidence that HN is deteriorating in terms of positivity. I really need to re-run that analysis and bring it up to date, because I believe that we will see a sharp dip in the last 9 months. Between SOPA, Jobs' death, and all the other calamity that's happened, I certainly imagine it is getting darker here lately.
Secondly, I've put forward a few attempts to combat this. One approach is to change the way the karma system works [2], so that it rewards people for consistently being upvoted instead of the sort of lightning-bolt comments that tend to yield an exponential or maybe even bimodal distribution.
Another approach is to detect and flag anyone who is frequently rewarding malicious comments [3]. The system I put forth could be done either by manual flagging or implicitly by looking at co-occurrences. It was originally designed for articles, but as I noted in the post, it is trivial to adapt it to comments.
Now, in all these cases, the articles were on the front page and a lively discussion ensued. Yet nothing. Ever. Changes.
PG explicitly said he was "considering" the honeypot approach. I don't know if he's actually implemented it, since it wouldn't be visible to non-admins. I will guess that, since he's a busy guy and we still have these discussions periodically, he has not. Fine.
Why would you expect things to change course then? Or if you didn't, why are you all acting surprised now?
A site growing at super-linear speed is going to be very prone to these affects. If you do not put forth an effort to combat the influx of lower-quality comments, then you will see your site slip away.
[1] http://blog.effectcheck.com/2011/05/31/do-social-news-sites-...
[2] http://www.nashcoding.com/2011/08/23/how-karma-should-be-mea...
[3] http://www.nashcoding.com/2011/10/28/hackernews-needs-honeyp...