Bitcoin is hardly cost prohibitive. When was the last time you sent a transaction? The last one I sent cleared at 2sats/byte and was <$1. Are you going to buy your coffee with it? No, probably not, but that hardly makes it a useless as currency replacement. Replace-by-fee doesn't make small transactions any less trustworthy either, since you should never trust any unconfirmed transaction (by definition, if its not on the blockchain its not yet a transaction). Furthermore, the lightning network blows away the competition in terms of cost per transaction, and while not perfectly trust-less (unlike the base layer) it has far less custodial risk than a bank or credit card account. If for example your counter-party goes rogue, at worst you just close the channel resulting in a rollback to the last settled balance state, minus an on-chain fee.