Technology

It absolutely is relevant.

The government shouldn't be able to know whether I'm buying toilet paper, ammunition, or anti-government books. There should be no way to track purchases to me unless I opt-in and provide it (e.g. register for a warranty, submit to background check, etc). They don't need to know both sides of any transaction to enforce any law, because that would be a violation of my 4th amendment rights (or whatever privacy/anti-search laws you have in your country).

I happen to not commit crimes, generally speaking, but that's completely irrelevant to the discussion about whether my purchases should be in the clear. Ideally, everywhere would accept some form of privacy-oriented cryptocurrency, like Monero. How money gets from me to the vendor is completely unrelated to law enforcement, all they need is a record of transactions for tax purposes, and there's nothing stopping the store from tracking that in the same way they do cash. If they suspect someone of a crime, they can do old-fashioned police work and prove it (e.g. subpoena camera footage, station officers at the scene, interview people, etc).