Tracking us all over the Internet is useful, if you're a spammer who wants to hassle everyone to buy their junk all the time. Most of us don't like spammers, either.

The privacy concerns should be minimal.

Please correct me if I'm misunderstanding you, but you appear to be advocating the collection of arbitrary information, via a third party script downloaded from an external source, in the middle of a payment process where sensitive credentials are in use, without necessarily giving notice to either the customer or the merchant about what is being done.

I normally prefer to make logical arguments and cite real data in this kind of discussion, but I genuinely don't know how to respond to the suggestion that this has minimal privacy concerns.

I don't care for your attempt to scare an entity away from doing something quite reasonable.

You and I have very different ideas of what "quite reasonable" means. Indeed, this "quite reasonable" behaviour seems to be illegal on several different grounds here in the UK, and as a merchant I would worry not only that I could not trust any third party service doing it to treat my customers well but also that they could get my own business caught up in at best dubiously legal activities without us even doing anything. That sort of ambiguity/distrust is toxic and grounds for staying far away from any such service.

Do you actually have any evidence that Stripe is in fact doing this kind of thing, or were you just stirring up trouble?