We need to go after Collective Shout and the payment processors in this case. They're overstepping here, not the storefronts. Steam and itch can't really do much if the threat is "do this or you can't sell anything on your platform anymore", other than pivot to crypto which the vast majority of customers are not gonna do.
In the US, there's the "Fair Access to Banking Act".
There's also this petition which everyone can sign: https://www.change.org/p/tell-mastercard-visa-activist-groups-stop-controlling-w..