MC/Visa wield a great deal of market power, which is bad because they become directly controllable entities.

I can't believe I am about to say this: Bitcoin fixes this.

Some other cryptocurrency fixes this, maybe (big maybe). But as long as _Bitcoin_ is seen primarily as an investment opportunity it can't really function as a means of exchange. For the same reason that we expect and need USD to lose value over time, people need to be encouraged to exchange their currency, not sit on it forever.

Something doesn't need to be perfect to be an escape valve.

So for example, when backpage's speech was unlawfully suppressed by the US government via payment processors cutting them off in Operation Chokepoint, they successfully adopted Bitcoin.

... and then Kamala Harris aggressively prosecuted them for 'money laundering' for the evading the payment processor blockade, even though her own internal staff report said they were guilty of no crime and were a treasured asset of law enforcement in the fight against human trafficking ( https://reason.com/2019/08/26/secret-memos-show-the-governme... ). So aggressive was the prosecution that they caused a mistrial by flagrantly disregard of the court's orders, then prosecuted again leading the the suicide of one of the founders following a decade of vicious harassment by the state.

uh ... so maybe not the best example.

Or maybe it is the best example: The root cause in the abuse by payment processors is the US government leaning on them to abuse their subjective discretion to suppress lawful activity that the government is constitutionally prohibited in interfering with. This is both what underlies the schizophrenic response by mastercard, which likes money and would generally just prefer to process everything profitable, and is also why Steam would be taking a huge risk to route around them with alternate payment means.