You just ban Monero then. If something is a problem, and you want to ensure financial visibility then ban all transaction types that hide visiblity, like banning mixers. This is separate from whether it's a good idea or not.
I don't think you can ban people doing crypto entirely, but you can make the financial exchange points where cash goes in and out ever more difficult.
It’s in the process of being grey listed. Similar to running an all-cash lifestyle, it’s possible. But you’ll have your money frozen and seized and stolen from time to time. And you will hit intentional roadblocks any time you attempt a major financial move.
You just ban encryption, then!
You just ban liquor/drugs, then!
Monero making law enforcement investigation more difficult due to privacy algorithms does not make it legal to ban.
You cannot ask ransoms in a currency the victim cannot access.