This. Same with Facebook. Even if I choose to not use a particular service, these services still know about me because so many other people I interact with do use these services. I get that as a Gmail user, you've agreed to allow them to read emails for whatever they choose. However, I did not. If I hit reply to a Gmail account, I'm not agreeing to the ToS. Just because I visit a site that has chosen to use G*/FB does not mean that I agree to the ToS. A website's cookie notices give me the option to leave if I don't agree, but by then, all of the tracking has already started without my agreement.