> making my life worse

> technology improves my life in many ways

First of all, it might not be about you. If you are privileged enough to not have to worry about being the target of prejudices, hatred, or the occasional witch hunt, then you might not see the necessity of keeping secrets. Some people are not that lucky.

> making my life worse

It probably isn't making your life worse at the moment. Right now we have barely scratched the surface of what is possible. Most of the current uses are fairly benign (such as ads). The concern isn't about current uses. The problem is the open-ended risk of anyone abusing that data in the future.

You are essentially making the bet that either 1) nobody will ever invent a use of your data that is harmful to you, or 2) nobody will ever abuse your data, or 3) that your data won't actually live forever. Clause 1 is already broken in some areas, clause 2 denies human nature, and clause 3 has a lot of evidence suggesting data rarely disappears.

> something tangible

Ok, lets consider insurance companies and/or banks. These businesses would really like more to get their hands on data that could give them excuses to raise your rates, deny your loan or insurance coverage. Sure, we have laws and regulations that theoretically prevent some types of data from being used. The legal situation becomes less clear when none of the prohibited data is used directly but it can be inferred from other types of data that is.

If you think this is a theoretical concern, then you need to read about the deplorable practice known as "redlining"[1], where data was used as a cover for racial hatred and forced segregation. We already see problems with various types of data being used in police work and judicial situations where certain combinations of "unrelated" data is actually a reasonable proxy for race.

Can you say with certainty that a future insurance company won't be able to take all of the data points you've been generating in ad networks - with absolutely no "PII" - and find some pattern in your history that can be used as a reason to raise your rates? Or deny coverage? This is only one stupid example; it will be a lot more subtle as we learn new analysis methods and creative data manipulation methods.

However, you asked for something tangible, so you should look at this[2] map of Amsterdam. Each black dot on the map represents 10 Jews. The Nazis commissioned this map from the local civil servants that managed the census data. I doubt they thought that their recent change to the census to include a question asking for religious affiliation could ever be dangerous. 3/4 of the dots on that map were murdered in the camps. Yes, this is an extreme example. I hope ad tracing data won't end up being used for that level of evil. Unfortunately, there are a lot of possibilities between "serving an ad" and "genocide", even though they are both data problems.

> Why would an ad company sell user data when that's their entire competitive advantage?

Selling data can become another source of revenue if the company has significant financial problems. Given the recent-ish trend of companies to agglutinate into a single power (or small group of powers), the transfer of data might be "internal" instead of a sale. Also, you're assuming it would be the ad companies choice; bankruptcy courts may see it as a valuable asset to be liquidated, and governments may simply take the data using various methods.

[1] https://en.wikipedia.org/wiki/Redlining

[2] https://www.verzetsmuseum.org/uploads/archive/museum/topstuk...