Why should google care?
As long as there are 10 non-spammy sites on the front page, it doesn't matter that some more quality sites got ****ed by a douchebag spammer.
This is not an ethics game, google is as blackhat as the neg-seo-ers. If you don't like the game don't play it.
As for me on of the few things I wouldn't do in SEO for moral reasons is indeed neg SEO. However I still think it is not as bad as promoting pharma products to people who don't need them, which is considered normal amongst IM-ers for some reason :/