I was being flippant, but isn't that true of anything though? How do you know Linux isn't secretly reporting all your activities to Big Penguin?

You should be able to trust a popular open-source project, because you trust that there are folks who will go in and take a sticky beak at these kinds of things. This why a lot of security folks prefer open-source software over close-sourced solutions.

Surely, if Chromium were cross-correlating profiles, then it'd be on the front page of Hacker News in short order.