> Why are payment processors/banks bad again?
It's a matter of opinion. However, the only reason for bitcoin to exist is to avoid banks and payment processors. Hence it's illogical to make heavy use of coinbase/etc. regardless of what opinion you have.
Bitcoin has many downsides (volatility, no recourse, vast energy usage, paranoid wallet security, high fees, long confirmation time, etc.) and one upside (no need to trust processors/banks).
If you think that processors/banks are bad, then you might find that the upside outweighs the downsides, and make many on-chain bitcoin transactions. Yet you shouldn't use coinbase/etc. in this case, since they're a bank/processor, hence you'd be removing the only upside that bitcoin has.
On the other hand, if you don't think that processors/banks are bad, then the upside of bitcoin isn't worth all of the downsides. You might as well use regular currency, with all of its advantages over bitcoin (instant payments, lower fees, lower volatility, recourse, less paranoid security, etc.). In this case there's no need to use coinbase/etc. because there's no need to use bitcoin.
Those intermediaries do serve a role in converting between traditional currencies and cryptocurrencies, but it only makes sense to use them occasionally, e.g. buying a stash of bitcoins and immediately 'withdrawing' them to your private, on-chain-only wallet. If you're regularly converting back and forth, or maintaining a non-zero balance on their systems, you would always be better off doing something else (either sticking to fiat, or sticking to crypto).