Why Is Full RBF Controversial among Some Cryptocurrency Users and Merchants?

Full RBF is controversial because it completely removes the limited security offered by zero-confirmation transactions. Merchants who rely on instant 0-conf transactions for point-of-sale purchases (e.g. buying a coffee) face a much higher risk of double-spend fraud, as any transaction can be replaced with a higher-fee conflict.

Opponents argue it hinders Bitcoin's utility as a fast payment system, while proponents argue it simply reflects the true, unconfirmed nature of 0-conf and improves the fee market efficiency.