Why the lighter burden is credible:
FinCEN guidance distinguishes unhosted/software wallets from custodial ones. If end users hold their own keys and you don’t accept or transmit value on their behalf, you are generally not considered the money transmitter. In a user-controlled (non-custodial) model, Circle gives you the infrastructure, while you remain responsible for sanctions/KYC policies and tax reporting for your counterparties.