Itch is not to blame, they are victims. This isn't the first time something like this has happened. Previously it happened to OnlyFans and Patreon. Both platforms capitulated to the demands of payment processors, because it was the correct decision. The demand wasn't remove NSFW because we wont authorize transactions related to them anyways, it was "REMOVE NSFW CONTENT OR WE WILL REFUSE TO AUTHORIZE ANY TRANSACTIONS RELATED TO YOUR SERVICE."  As you might guess, platforms like OF and Patreon aren't funded by good vibes and fairy dust, they need MONEY, and losing access to digital financial processes would be lethal to these platforms.  Don't waste you time, energy, and attention blaming a group that had zero reasonable and viable alternatives to the action they have taken, direct your efforts to actions and activities that will fix this:

For the US users: https://action.aclu.org/petition/mastercard-sex-work-work-end-your-unjust-policy... 
For the UK users: https://petition.parliament.uk/petitions/722903

Everyone else needs the support of the payment processors infinitely more than the payment processors need us. Unless we magically make a new payment service, or get relevant legislation passed into law, this will keep happening because no business is going to commit digital suicide for moral high ground, it would be pointless, wasteful, and self-defeating. Itch supported NSFW content before, they will re-extend support once their platform and ability to do the thing they exist to do is no longer threatened.

I only know of the existence of Itch, because of adult content. They better survive this. GameJolt transmuted into a advertisement hellhole that sells users like a pyramid scheme, after they purged adult content.

It is those English speaking countries and their irritating mindset that it is ok to govern which fictional content is legal and that it is somehow ok to be non-neutral as a payment processor. All fictional content is supposed to be legal! Even the disgusting ones about things that are illegal if it were real. 

It is my money, not the money of the credit card companies. I demand they be neutral and stuff whatever political or ideological agenda they have, where the sun does not shine. Such agendas might be enacted on a platform level, not on a service provider level. And even then I would not like it very much if a platform pushes agenda. Any agenda. I can decide for myself, what I chose to play on a platform, I do not need the help of the platform to chose the "correct" fiction.

Patreon for example shuns incest content. Fictional incest... Meh, whatever. It is a platform. There are other places for people interested in smut like that. And that stuff would even be legal in real life in places where lgbt things are not all that legal https://worldpopulationreview.com/country-rankings/countries-where-incest-is-leg...  . Oh the irony.

I hope the international bank transfers are developing faster. The only reason why credit card companies still thrive is momentum and horrendous fees for international transfers. Within a country bank to bank transactions are a lot cheaper than credit card. Credit card companies are a mere infra structure buffer and might become quite obsolete in the future. They should not anger their customers.