a) One way or another, that's "not letting them enjoy the same freedoms as other companies"

b) How would you then prevent them from re-amalgamating the way Verizon and AT&T did after the Baby Bell breakup? Not just for a few years afterward, but ever?

c) I think that payment processors actually make a pretty convincing natural monopoly: consider that if we had 400 payment processors with no common interface protocol between them (and let's face it, without being forced to, companies aren't going to make such a standard), your Baby Visa #27 credit card wouldn't be accepted at a merchant who only accepts Baby Mastercard #100-200 cards. And even accepting that many different payment processors would be pretty onerous.

Remember, this isn't the card issuers we're talking about; this is the backend processors. The only reason our current "universal" credit card infrastructure works is because nearly everyone takes Mastercard and Visa, and most credit cards—and many debit cards—are either Mastercard or Visa. Sure, it would be possible to create some kind of an interchange standard that all 400 processors would follow, but again, where's the incentive for any single processor?

> How would you then prevent them from re-amalgamating the way Verizon and AT&T did after the Baby Bell breakup? Not just for a few years afterward, but ever?

By continuing to enforce anti-trust legislation, though this time on the opposite M&A end.

> I think that payment processors actually make a pretty convincing natural monopoly

I guess I don't know enough to make an authoritative statement here, but I don't personally find this argument super convincing. I expect the actual breakup would be on the order of like 6-20 companies at most, and it wouldn't be rocket science for some middle-man to abstract out the processing. We solve many harder problems than that in the software industry every day.

But either way, it's a valid argument, and I think a court would be the right place to duke it out. If they are indeed a natural monopoly, then I agree it would be appropriate to start placing limits on their behavior.