Companies' ability to track people online has significantly outpaced the cultural norms and expectations of privacy. This is not because online companies are worse than their offline counterparts, but rather because what they can do is so, so different.
Not only are these (numerous) companies getting better at tracking us, a lot of times we're unsure of what the privacy expectations should be around that tracking. But Madrigal anticipates where the uncertainty leads if we don't set cultural expectations on online privacy:
The current levels of machine intelligence insulate us from privacy catastrophe, so we let data be collected about us. But we know that this data is not going away and yet machine intelligence is growing rapidly. The results of this process are ineluctable. Left to their own devices, ad tracking firms will eventually be able to connect your various data selves. And then they will break down the name wall, if they are allowed to.
Another fantastic article from The Atlantic.