You are subject to the ads chosen by the websites you use. You are compensated in the form of the service of those sites. Google is just incidentally the ad provider the websites you visit choose to use. All assuming you don't block of course. The comparison to unpaid labor is still unapt. Unless you are gaining no value from these sites that are showing you ads? If so then why do you keep visiting them?
Now you're complaining about a different thing. A thing which I'm not even sure happens. I know for a fact you can disable ads personalization, which should eliminate all incentives for google to track you, in the event that they were doing so before.
As to the rest, people have different views on the ethics of these kinds of voluntary interactions.
