I'm a big fan of card payments myself, but I agree that cash should be accepted universally, until unbanking/underbanking is completely solved and there is a cash-analogous private way to pay.
Besides the accessibility issue, not nearly all activities or situations making somebody want to transact anonymously are illegal (just consider e.g. people in unsafe domestic situations trying to get help/away but not having their own card).
I believe we could strike a pretty good balance with some research, engineering, and product development, avoiding both possibilities for tax evasion and financial crimes on one extreme, and creating a complete financial panopticon on the other.
