It would seem to me to work both ways. If suddenly Google started seeing lots of email passing through about “gun rights” and “anti immigration reform” then the gathered data could be skewed in that direction.
If millions of gun owners start searching for “ruger mini-14”, or 5.56 rifles that would certainly trigger some data mines.
Data mining in and of itself assumes that the data they are mining is clear and random. Just like we Freep polls people should be able to freep the mine.
Just takes a large number of people who are dedicated to completing the task for 5 minutes a day.
I think this is all “pollyanna”. They crawl all websites and documents to obtain the raw data for THEIR OWN USE. What YOU see is highly likely skewed to what THEY WANT you to see. You are not allowed unfettered access to their raw datasets. They mine their data and make the results available to you, in the way THEY want.