You're not opting out of Google simply not using their service though. You're using Google invisibly just by visiting most major websites or by using a lot of (non-Google) software which integrate their services.
Facebook is mostly blockable on an individual basis, but Google really isn't. There are so many vectors:
- Google provides a geolocation service for applications to locate you by triangulating you relative to nearby wifi hardware. This sends data to Google about your devices wifi hardware and the ssids it detects. This isn't an in website feature, so normal content blocking doesn't help, it will be an application setting. Firefox and Safari both used to use this (Mozilla have now created a competing service).
- Google provides suspicious site screening services ("safe browsing" advisories) to many applications, including browsers.
- Google hosts most of the CT logs. I'm actually not 100% sure how the mechanism works here in detail, so this may eb a red herring, but it seems to be that browsers may periodically send a list of https sites you visited to these log servers to audit the certs for those sites
- Google provides free fast DNS which sends all of your DNS traffic to their servers. This may be set by the administrator of the network you're connecting through.
- Google analytics is used by many non-browser applications, and also in areas of the browser not covered by content blockers, e.g. Firefox's add-ons settings page.
- Many sites use Google js cdns and ajax apis for required functionality, so a content blocker will need to set whitelists to get the site to work.
- there are more such things, these are just examples
Facebook does none of the above.
Something like Decentraleyes will help with the cdns and a custom firewall, hosts file, filtering proxy or things like Little Snitch can help with some of the others but none of these are trivial.
In my eyes the CDN was the hard thing among those, as I'm not sure how many of them Decentraleyes manages to replace. Most of the others, though, are either blocked/not used for me, or used because I feel there are benefits (i.e. not through social pressure), namely the safe browsing advisories.
