> third-parties who can make all sorts of decisions based on a made up story about who I am, my preferences, my values and whatnot

You're going to be presented with ads and preyed on by marketing no matter what. The "made up story about who you are" is just even more imaginary the less they know about you. You'll simply be presented with less-targeted ads.

Not the point, no one benefits by having an accurate (or non) dossier built on them, up for sale. The drawbacks may be infrequent and postponed but as history confirms, quite real.