lokedhs said "ostensibly" because the internet advertising industry has long maintained the pretence that tracking users and showing them relevant ads is helpful to the user, when the truth is the advertising industry cares about the opinion of users like the thanksgiving industry cares about the opinion of turkeys - which is to say, not at all.

There's a reason these things are opt-out rather than opt-in.

The answer to marcus0x62's question - why would a person want advertisers to correlate their behavior - is that they wouldn't, and if they want to advocate for their own self-interest they should install an ad blocker.

If it's the goal, you'd expect ads to be actually be more relevant and useful to users.

They don't, which has been shown in studies. What has been shown is that showing the same things people already bought give people regret which increases total amount of purchases.

In other word, the goal is to not to give users a good experiences watching ad's. It is to make them buy more, which is an orthogonal goal.

Let’s say you’re DHS. You contact some person and have a conversation like this

Govt: “I need IP addresses, ideally cellular and known public wifi, of a person using this email address”.

Data broker: “Here’s the list including the most recent cellular IP address associated with that person at this timestamp and their most used public wifi locations.”

Govt: “Hey, cellular provider, where is this subscriber right now?”

Provider: “Here’s the lat/long, last seen 1 second ago. Happy hunting!”

I disagree: The main problem with advertising is with its primary goal, which is manipulting people into excess consumption. There are of course other secondary issues as well, but even without them ads are already a net negative for society.