You've been drinking the Google kool-aid. Google has always been the primary financier of web spam on the Internet. They knowingly profit from Adsense on spam sites. If they wanted to, they could end web-spam over night by banning Adsense accounts for spamming.

SEO is just another form of marketing. It is no more/less legitimate than PPC campaigns. In fact, PPC ads are far worse because Google does little to police them. As long as Google makes money, they don't care if you scam users. That's why they paid half a billion dollars in a settlement to the FTC for knowingly selling illegal pharmaceutical ads.