But those aren’t private, right? There’s an entity in the middle that can see all the purchases I make.

If I use one of those to send you $500 right now, the entity in the middle can see that I sent you $500 but nothing more.

That's too much for me. It adds up to that entity having a record of all my transactions, who they're with, and how much they are. Def not private like cash.

Is it just the principle of it, or would fully private transactions solve an actual non-criminal financial problem?

A product that's a violates my principles _is_ a problem.

More practically, being surveilled creates a data store about my life that can last forever, theoretically. It's hard to conceive how that could be used if (when) that data gets mishandled. Might as well not leave a trail.