How has todays technology blurred the lines between whats public and what's private

Well, not only is our data bought and sold, It is also used without consent. The key to stealing data is technology, most data is input through some sort of technology. Whether it be someone entering their DOB on a website, or using their credit card for an online purchase. There are some sites that have even confirmed selling their member's data. As to why they do it? I'm not sure, some people believe it's to pander or better aim future products at individuals.