Oh sure, technically speaking especially in the US you can sue anyone for anything. I can sue you right now cause I think your username is dumb (I don't, just an example). But that doesn't say anything to the chances it actually going anywhere. Are there a lot of people that have been harmed? Sure. And does there have to be a literal law that's broken, no. But there has to be a generally understood legal precedent.
For example if Flubber was real, and released, and it turns out exposure to it gradually causes severe mental illness, there's no literal law against that. It's a new circumstance. But there are many, many precedents against poisoning people via exposure to something. Again, neither of us are even close to lawyers, but I don't think there's any precedent to build a case on here. Visa, like most businesses in general, is free to do, or not business with whoever they like, for whatever reason, at whatever time, subject only to the clauses in their own contract. The only exception to this is, again, if they're engaging in discrimination in the range of a protected class (sex, sexuality, race etc). You can SUCCESSFULLY someone in a class action for poisoning you because poisoning is illegal, and has been for a very long time. Visa's actions have caused a great deal of financial harm to a large number of people, but unfortunately I don't think they're a breach of either their contract with Itch or generally established law. A landlord kicking you out of your rented physical storefront also does massive financial damage to you, but you can't successfully sue him as long as he's abiding by relevant eviction law and the lease that was signed.
Believe me, there's a class of lawyers that flock to any situation where a class action actually has even the slightest possibility of going somewhere. They'd be all over this if that was the case here.
I appreciate the sentiment though. I just don't think there's anything to go on there. If there was, the CCC would have been sued ages ago, this has been going on for a very, very long time. And they HAVE been sued for many other things, but mostly of the "being a monopoly and crushing competitors, overcharging people etc variety".