This is disingenuous, I suspect that you know why. The reason few people would opt-in is not because few people support or agree with the premise. The reasons is the very act of "opting-in" to a thing is a huge barrier.
If receiving CPR was "opt-in", I would expect 1/3 of the population would just never get around to it or somehow be confused with the process. I bet you even could drive the opt-in rate down to 10% just by requiring a separate paper form that had to be requested and mailed to specific address.
Targeted ads are a method by which lots of people are able to make a bit more money. These aren't exciting changes but it is the difference between lots of people having hobby and making it their job. As most people don't care enough about the privacy of their internet history to take trivial steps like using private browsing windows. Why should the obligation to be on the large number of people who don't care when the small number of people who do care can take trivial steps, like private browsing?