Honestly, I don't see how open/free software can fix it. For example google analytics is commonly used through web, source code of the tracker is available as raw text in javascript, and where is the promise of open/free software? Sure one can install tracking blocker (like ghostery), but just because the track itself is open source (most pages source code is accessible as raw text) - tracking hasn't been magically fixed for web, and people still play cat-mouse with track blockers. Given this example I don't see how making something open source or free software suddenly fixes that. Indeed, yes, it does makes it easier to audit software, but that's about it. One might say that one can personally audit all the source code, but there is practical limit to how much we can do it - a common system might run 20k+ packages with million lines of source code, and even if we trust all major dependencies, tracking can always sneak-in through 3rdparty libs, downloadable code (aka js), etc.

In my opinion a better tool would be a legal framework to limit companies what they can and can't do. For example EU GDPR is much stronger factor in limiting what companies can do with personal data, and it forces companies to provide opt-out option (and proper opt-out, not like "we use cookies, if you don't like - please leave"). The reason why EU GDPR is not a joke are fees - 4% of global revenue (or 20 million EUR, what is bigger), so companies are forced to comply. I would love to see a proper legal framework for opting-out from tracking, but looks like it will take another 10-20 years to develop it :(