Actually, Google's goal is to provide relevant search results. But their goal is not to provide the most relevant search results without wiping out any "innocents."
The surveys on relevance almost always look at the top 10 results for any SERP and get a % of them that is relevant. Google could afford to wipe out a lot of "innocents" in order to make sure that the top 10 are all relevant, and I believe they have incorporated this into their core philosophy.
I believe they would rather have 10/10 relevant on the first page with XX% of the good sites wiped out than have 8/10 relevant and not wipe out any "innocents." This appears to be a major philosophical shift since the Florida update.