I don't think that's quite true. It is not a straight common sense equation, largely because 'it's free' and so people don't apply a complete value rationalisa

I don't think that's quite true. It is not a straight common sense equation, largely because 'it's free' and so people don't apply a complete value rationalisation to using those services or even understand the implications of the deal they're agreeing to. If Facebook, Twitter, Instagram etc were to actually charge fees for the cost of running the services without the advertising/data harvesting cover, I wonder how 'valuable' the perception would remain...