If Google wants to fight against SEO (of whatever color of hat), it needs to somehow separate the links of people that are trying to manipulate Google and the links of people that are just trying to use the Internet.

The closer a spammer's actions appear to that of a normal person, the harder it is to find and devalue those links.

Google's updates have been in the recent past are saying (Panda, Penguin), "Well, spammers generally tend do to this, let's make that bad now."