why your ebook is not a book

People mistake ebooks for books. In reality, an ebook is a data collection tool dressed up in a moderately entertaining narrative.

This is why used ebooks don't work: How do you reset this data collection tool when it's resold to another user? 

The original purchaser of the ebook most likely used a credit card to buy it.  And an email address.  And possibly an iTunes, Facebook or Twitter or other online social media account that allowed the purchaser to share quotes, thoughts and critiques from the reading of the data collection tool dressed up in a moderately entertaining narrative..

Kobo is just starting conversations with publishers about sharing its data. "Publishers are asking, 'What are people engaging with, and how are they engaging?'" - source

"We do have people tell us that what they love about Kobo is that they can sit on the subway and no one knows what they're reading – it does provide some element of privacy." 

I guess. Until the publisher decides to promote the title to all the other readers through the reader or an app on an interactive billboard: "Someone is being naughty and lingering on p. 142 of Fifty Shades of Grey. Quick, everyone, download the book now and see what's got someone on the train with you all hot and bothered."

"Gathered data is aggregated and anonymous." Right. If you say so.  But like any device that can deliver content, an ereader is just another tracking device for computers to monitor our every movements: 
Where were you when you read that book for 90 minutes?  At the airport?  2,000 miles from the address we have on file for you?  [At this point, the computer is programmed to go, Hmm.]  How many other devices were near this one?  Can we assume these people know each other?  Let's see if we can find other locations where these devices have been in proximity to each other. [The computer makes yummy sounds.]

So if publishers begin to allow users to sell pre-owned ebooks, then what will happen when all this data get dirty with other users?  Users whose credit cards are not known because the transaction was done through a third party? Now all those reading patterns and locations become worthless.

So enjoy your tracking device. And know that when you gaze long into an abyss the abyss also gazes into you.  And tells you what to read next.