Also that's not a reason to ban certain genres/kinks, which is what's happening here.
But it is possible that Visa sensibly and correctly said "anyone who makes or purchases such a game is a despicable scumbag, and we shouldn't assume the financial risk of dealing with them."
Or you think one person did that and it made the credit cards decide any story with incest would be the same? That would be ridiculous on their part.
My understanding is that payment processors are obligated to follow the policies of Visa/MasterCard, AmEx, and Discover, but that those parties' policies don't explicitly ban these specific things for sale. Instead, they "strongly encourage" processors to ban them in their user agreements under the implicit threat of their risk level being increased, which in turn impacts the fees they pay to the credit card companies.
I've not been deep in this world since ~2014, but at that time the only processor I could find that wasn't specific to the porn industry, offered physical terminals, had reasonable (if high) fees, and didn't ban legal transactions in their user agreement was PAI ("Payment Alliance International"). A quick look at their site today shows that they seem to have been acquired by Brinks, so that may no longer be the case.
My hot take take: Crypto still fills a valuable role, and will still "take over" the global financial system both at the individual and institutional level. Whether that's Bitcoin, another coin, or something new created by the institutions themselves is yet to be seen.
You're right that it's "tainted", of course. That's why I think we're in a (hopefully) long slump in adoption. I think that will rapidly change if and when the US Dollar loses its place as the world's reserve currency.
At some point there will be a war or significant political disruption. A large part of the world will want to divest itself of dollars, and none of the state-backed alternatives will be stable enough for their needs. That's when we'll see a shift to crypto - first some international institutions that do business across ideological borders, then the rest of the internationals, then individuals.
Unless and until that happens, things will continue to slowly grow. The boom/bust cycle will keep going, getting longer and lower magnitude over time. There's still money to be made in speculation, but that's not what interests me :)
Sorry how would crypto end up more stable than any candidates for a reserve currency? The only thing even remotely stable in the crypto world are stablecoins which... are pegged to the dollar (the actual reserve currency) which is already unstable in your scenario.