Earlier quoted context omitted.
Google knows that when I type 'rails' into their search box I mean Ruby on Rails and gives me relevant results, instead of railroad tracks or hand rails. It's not a big leap to think they'd do that globally for extreme results like DS where most people want to know about them and not actually visit the site.
So at what point will Google look at your search history and decide that you are looking for racism when you search for a racist term? I don’t think anyone on here will admit if it’s happening to them, but if the answer is never then that means Google is suppressing the “best” search results due to political reasons. For a less charged example, Google won’t show pornography as the first result for a fetish term, ever…
Given that there are definitely people that I have personally met that keep complaining "they keep getting racist results" in Google and Youtube, I'm guessing we are already there. As for how they build up this profile, I'm sure the people that actually know aren't allowed to tell us.