The main reason for the nature of credit-card fees (fixed+percentage) is to manage the fraud.
Stripe's simplicity of access means that it is going to be completely destroyed by fraud. The reason for the effort in getting merchant accounts is that if you take the money and run, the organization that gave you the merchant account is responsible for the chargebacks, up to 6 months later.
6 months is a long time. It's not feasible for most businesses to wait that long to get their money. Hence the percentage charge to cover the risk of fraud. If you think that a 2% charge means that 1 in 50 of every transactions is fraudulent already, imagine what a skilled fraudster will do.
Stripe's simplicity of access means that it is going to be completely destroyed by fraud. The reason for the effort in getting merchant accounts is that if you take the money and run, the organization that gave you the merchant account is responsible for the chargebacks, up to 6 months later.
6 months is a long time. It's not feasible for most businesses to wait that long to get their money. Hence the percentage charge to cover the risk of fraud. If you think that a 2% charge means that 1 in 50 of every transactions is fraudulent already, imagine what a skilled fraudster will do.