This is hilarious. A forum called BLACK HAT SEO discussing whether Negative SEO is moral/legal or not. So it's okay to take a site selling replica Rolex's HIGHER so it ranks right next to the real Rolex, but its not okay to push Rolex LOWER? It's okay to break these Google rules, but not these rules? I get it, legal is one thing, Google's rules is another. But think about it. Granted Rolex will come after you if they had a clue, but what a nightmare for the lawyers to try to talk to the SEO geeks and get a judge to actually understand what's going on and actually prove anything. You'd have to be able to produce records of correspondence showing an agreement was entered into to harm another business or entity. How they did it (what techniques, links, etc.) would be almost a moot point. If the people were careful, good frickin luck proving anything. Next to impossible.
Manipulation of the SERPS is manipulation of the SERPS. It's up to Google, their thousands of engineers and their billions to figure it out. Until then, there's nothing wrong with essentially exploiting imperfections in their algo, beit it for increased rank or decreased rank. I for one am looking very forward to Negative SEO growing in leaps and bounds just to see what Google does. Penguin was just a scare tactic to try to stop people from massive backlink fabrication. They have already started to gradually roll it back in my opinion, probably because of an increase in Negative SEO. Their only solution is to decrease the weight of backlinks in the algo and hire more Indians for manual reviews.
What you don't see here is a lot of people willing to admit they are doing it. A lot more than you think.