>Wouldn't high fees be competitive? A lot of incentive to compete there. Anticompetitive would be setting the fees too low to compete with.

Canada has a debit card network called Interac. Last I checked, the transaction fee was typically a flat $0.10 CAD (~$0.075 USD). There are shops that do debit or cash only, but it's not the norm (typically restaurants and niches with high chargeback risks). I am curious what keeps credit card acceptance high in Canada, despite a very widespread mature card network. I assume part of it is that consumer debt increases spending volume overall, but that can't be the primary reason I feel.