True, but how high is the chance that somebody that can't handle a $400 emergency today will be able to pay back $400 of credit card debt next month? And if they don't, they usually end up in more problems down the road.
Also, there is nothing that says you couldn't use a debit card for normal spending and resort to using a credit card only for when you actually need credit (assuming that the rewards inefficiency gets fixed).
I was answering in the context of the difference between chargebacks on credit cards vs debit cards. You aren’t out of your money while waiting on a chargeback to be processed when using a credit cards.
You're out of $400 of liquidity (until the issuer provisionally credits your account, which they are required for credit and debit alike) either way.
The only difference is lost interest payments for these ~5 business days (which the issuer might even have to reimburse as well; I'm not too sure about that though), as well as not being able to pay for cash-only expenses using the money in your bank account.
Also, nobody is saying that people can only have one single bank account, and a debit card linked to it with no spending limit attached to it.
Also, there is nothing that says you couldn't use a debit card for normal spending and resort to using a credit card only for when you actually need credit (assuming that the rewards inefficiency gets fixed).