Matt doesn't want to admit it but we all know it's true. The algorithm punishes shitty links and they can't tell if those shitty links were generated by me to increase my ranking or by a competitor trying to harm my ranking.

Or even whether the site they're punishing is the real target of the SEO at all. For example, there are a bunch of spammy "software index" sites that are basically just lists of free software applications trying to rank highly for people searching for that kind of software. It appears that Google has been penalizing the official websites of some of the software listed on those sites for being linked from lots of spammy sites.