If you want to withdraw more than 5k per day, you need to provide your SSN, Face ID and all the rest of it.
If they’re ever subpoenaed by law enforcement or audited by the IRS, your details are toast. So, the fact of the matter is if you’re looking for gains when/if BTC moons – you’re gonna be paying income tax on it.
Other than “owning my coins” I’m not sure what the big deal is. If I own my coins I am also at risk of sending to the wrong address, making some noob mistake. Whereas there is some protection there from coinbase’s idiot-proof interface.