I've had times when I was dirt poor, I mean DEAD broke, where having money in my account was a liability because I got a fine from my bank if I spent over a certain amount by even a quid and only having cash got me through.
Ethics aside:
Cash helps the poor make extra money they do not have to declare. Sometimes it's starve or look after your neighbours dog or child for an extra £30 quid in hand, or sell your mothers bracelet she gave you for rent money. That's the reality.
Cash helps struggling startup businesses keep more money for reinvestment
Cash helps immigrants survive who can't get an account. Frankly even the honest poor citizen sometimes struggle to get a current account or cannot get one. Quite disgraceful.
Cash helps vulnerable women in prostitution.
Cash helps the self-employed make money flexibly
Cash helps support the homeless
Cash helps charities
Cash helps fringe political parties and fringe political newpapers
Cash facilities the grey market and yes, the black market
Cash is flexible and cash is related to personal liberty.
You may be opposed to some or all the above, but like it or not all the above facilitates the economy. The economy is served by people having fiscal flexibility. Take away cash and people will resort to bartering. For women particularly that scenario has the potential to be very bad.
Removing cash is also a bad idea because it makes all your spend open to surveillance and vulnerable to being curtailed. If you think 'well don't do anything wrong then' it's worth remembering that what is 'wrong' is always open to change. We have seen that even in supposed democracies emergency powers have been drafted in to penalise people for protest by blocking their accounts. Not just on that measure, but attempts made to block accounts of people donating to causes considered politically unpalatable or the accounts closed by the banks themselves because of the social and political affiliations of the banking CEO. Nigel Farage a couple years ago had his account blocked and furthermore that personal information was leaked to a journalist. All well and good, but not when you are compelled to hold money in your account because there are zero alternatives. I will never forget those images of people in Greece lining up in front of their banks to try and retrieve their money when the economy collapsed, and the banks closing or refusing to allow them to empty their accounts
Cybercrime is being used as a source of soft warfare, and it looks like we are only increasing tensions with our neighbours. When your banking app goes down, or the central bank AI system messes up and you cannot get your money from the hole in the wall, you realise you do not, in fact, have money. You have theoretical money. You have numbers on a screen.
Getting rid of cash is a bad idea at the most basic level of community interaction. It's bad for personal liberty. It makes you 100% reliant on your bank, and on the human rights ethos (if you think byt the ordinary person won't ever have their account snooped on, don't forget the last government requesting banks inform DWP the moment a person on any sort of benefit hold money above the threshold for any reason and the right to check the accounts of affiliated persons to the account holder) an instant commitment of your government, and NGOs.
In effect I see cashless the way Americans see giving up the right to bear arms. You have no buffer between yourself and possible tyrannical government. No buffer between your hard earned money and targeted cybercrime, possibly less ability and agency to support causes or political parties that are socially or politically frowned upon.
Once we create that reality, and remove those freedoms the tide will never be able to turn back and we'll never get them again. You're left with bartering or some other means of exchangeable currency and frankly I don't governments or businesses would want that.