Very few people are blanket against any and all use of data about customers, or against any and all forms of advertisement. But most people really don't like companies harvesting their data in order to sell to other advertisers. Most people are sick of every company realizing they can make a little more money by advertising anywhere they possibly can, so now we're in a reality where the $2000 TV you buy in the store has pop up ads built in, records what you watch, and the company (LG in my scenario) will sell that data and use it to advertise to you more effectively. If you want to opt out entirely, you have to completely disconnect the device from the network.
Privacy and personal data aside, advertisement has strongly changed the consumer world for the worst. Nearly everything when a microprocessor tries to gather salable data, and now that can be everything from your toilet to your blender. You can avoid smart devices for the most part, but it's almost impossible to buy a modern TV that doesn't try to do anything except display video and audio.
As an example, there was (is?) a law that a video rental store can't share your rental history.
https://en.wikipedia.org/wiki/Video_Privacy_Protection_Act
Unfortunately I suspect that law didn't carry over to Netflix/AppleTV+/Hulu/Amazon/PornHub viewing history nor did/does it apply to purchase history like say Patreon/OnlyFans, etc...
I'm sure that limit is problematic as well. Various companies might want to hire a 3rd party to do data analysis. Should that be allowed? What about a service like Office 365 where there are 3rd party apps?
It's okay for a shop to optimize what they sell and recommend things based on customer data. What is not okay is for a shop to share customer data with any other third party.
Note that by third party I do not only mean advertisers, but I also mean hosting services such as Amazon, Google, Facebook etc.: if you think at them as long streets with shops on the sides, I do not think many people would appreciate having said street filled with surveillance cameras that track everybody's movement and purchases and sells this information.
Targeted advertising is innocuous compared to some of the ways your shopping history could be used against you. Imagine if health insurance companies could decline claims based on too many purchases of pizza and beer over the years. I thought this was supposed to be illegal, and I don’t know which laws apply now or have in the past, but ~20 years ago I did hear from a friend who worked in the credit card industry that he had seen this kind of thing happening. Has left me with nagging fears ever since. (I guess I should find out more so I’m not just spreading FUD :P)
In their fraud department.
As a software developer, part of that involved undergoing private investigator training.
It also involved utilising various consumer information databases.
The story I heard involved looking up an ex and seeing what kind of information was available. Not merely card balances and net purchases, but line-item detail.
This was in the early aughts. Which means that practices may have changed, but also that there is now vastly more information available.
Firms are not monoliths. There have been multiple instances of line workers, managers, and/or contractors whose interests have diverged from the firm's.
A number of eBay executives were convicted and sentenced to prison for harassing a couple whose newsletter the execs disliked (2022):
<https://www.cnn.com/2022/09/29/tech/ebay-exec-jail-harassmen...>
External hackers, thought to be from China, hacked Gmail largely seeking information on Chinese dissidents and Tibetian activists (2015):
<https://www.foxnews.com/tech/gmail-accounts-compromised-by-c...>
A former Twitter employee was charged with spying for Saudi Arabia (2019):
<https://www.theguardian.com/technology/2019/nov/06/twitter-s...>
And six Amazon employees were indicted for accepting bribes on behalf of sellers to distort the Amazon marketplace (2020):
<https://arstechnica.com/tech-policy/2020/09/doj-amazon-worke...>
So far as keeping contractors in line, even the NSA and CIA have had problems on that front --- Snowden and Winner, notably. Let alone their own staff (many cases of moles and foreign agents).
You are not in control of what others know about your shopping history. Your shopping history _WILL_ change when life events start up, and that's enough for advertisers to target you with new ads.
I'm sure a private individual doesn't like "leaking" this kind of data to others. But even if you didn't have an account, Web Browsers have cookies, your computer and internet has IP addresses, your credit card numbers and bank accounts also track you. The store (Amazon) will know your change of behavior and use that to bombard you with baby clothes advertisements.