I experienced this 1 week ago. Imagine you used your one and only debit card for a subscription service. The billing system of this subscription service went mad. Guess what: To stop this subscription madness you can only block your whole card. On top of that you have stress to get a new one from your bank and you are several days without a debit card. Or imagine somebody does a fraudulent charge... when it's large and the limit is not big (or connected to your account with a debit card) the money is first lost. You practically loose time where you cannot use that account/card anymore.

Right, but this problem seems solvable by having multiple credit cards. I would only make an online purchase with a credit card, never a debit card. If there is a charge that I didn't authorize, I can just click a dispute button on my credit card's web app and never have to think about it again.

The critical feature is you can specify a credit limit and expiry period for each virtual number. By keeping the credit limit at a bit above the purchase amount you dont' have to worry about losing a bunch of money if the number is abused, and by keeping the expiry at 2 months (12 months max) you avoid any abuse channels that would take more than 2 months to transact on the dark market.

edit: And of course you have the credit card company on your side to assist with fraud awareness and refunds. You won't get this with Paypal, Android/Apple pay, and especially not with any blockchain technologies where there is no intermediary working on your behalf.

I keep a Citi mastercard just for the Virtual Account Number feature and use it every time for online and phone purchases. The BofA feature has some severe issues.