Making everyone jump through hoops, at great expense, because the proceeds of crime are being laundered seems like the wrong way to approach stopping crime. I'd argue that bitcoin is in some ways more traceable, as all wallets are public.
Problem with KYC and AML is that if you listen to the regulators, there is no end to it, the requirements only increase. I was once asked to provide 20 years of banking receipts for a small savings account that my grandmother had opened for me when I was 5. In the EU at least, it's common for banks to block transfers between countries, even if the transaction is well-documented. The most infuriating thing is that there's no real proof that AML works. It's just excellent at false positives, ending in account freezes for innocent people.
Stablecoins' success is also a reaction to the ever-increasing friction created by overreaching regulation. If you have a supplier in China, and need to buy some in-demand goods, you can sign the contract and send the money now, whereas with the classic banking system, you'd have to wait for two weeks to clear everything. This alone is brilliant and should be welcomed for its usefulness.
What is interesting with stablecoins is that they are on the blockchain, which acts as a decentralized, uncensorable ledger which doesn't require you to tell a bank clerk what is written inside your wedding ring to be allowed to buy a second hand BMW in Poland.
The law says that banks need to do AML/KYC, a blockchain is not a bank, it's decentralized. Besides, being able to break a law can be good, when such laws have little to do with crime prevention, and more about feeding an industrial complex that earns from those frictions. And buying a car is not illegal as far as I know.
The main proponent that dictates the regulations, the FATF, is a shady, unregulated body that is used for political and economical repression.
it's not about taxes, it's about fighting illegal activity. Terrorist financing, drug dealing, human trafficking etc - do you really think it's a good idea to let those actors exchange payments freely?
Yes, I think everyone should be able to exchange payments freely.
Drugs should be legal, so that's not a problem. Terrorism and human trafficking are more complicated topics, but basically I think they should be attacked more directly, not financially.
If your concern is effective taxation, there are plenty of methods that worked historically while preserving financial privacy like property taxes.