I do this. The privacy aspect is just a bonus. The main advantage is I consistently spend less and have the world's easiest to manage budget with no forgotten spending, autopayment or contactless swipe. If there's £20 in my pocket after drawing out £50 I spent £30 no matter what I remember or what stuff I now have. I'm immune to 98% of supermarket special offer junk as I draw enough for shopping not shopping + impulse junk.
Done it ever since the dot con crash and we were seriously financially challenged for a while. Fifteen years later I haven't had the least temptation to revert, despite numerous offers of higher credit limits and more cards from assorted banks. Plastic gets used 0-4 times a month - for online shopping.
Despite all the hubris about cashless I don't find it the least bit inconvenient - everywhere takes it, everywhere I spend it has a cashpoint nearby. So all that remains for card and bank is online shopping and bills.
It's not all or nothing. Like any security (and confidentiality is one of the three pillars of security), there's no perfect solution but you can make it more costly for attackers. A few things that help for little cost:
* Use a pre-paid phone plan; don't give your identity to the telco. (Maybe not possible in all countries.)
* Use a VPN and/or Tor. Protect your browsing habits from your ISP.
* Use an ad-blocker or something like uMatrix to stop most tracking
* Pay for things with cash when possible. If it was invented today, we'd all be impressed with the technology: Complete trust between strangers, anonymous financial transactions - all implemented in paper; no encryption needed.
* Use one of the many anonymous, confidential communication services for chat, text and voice.
But I agree that the answer in the law, not technical means.