A post on Reddit proposes some action gamers can take to push back against recent reports of removal of adult content from Steam and from itch.io based on pressure from credit card companies. There's also a post on TheGamer pointing to another Reddit post where a gamer shares a response from Visa to a question about its policies. Surprisingly, Visa claims it "does not moderate content sold by merchants," despite it seeming that this is exactly what it is doing in these cases:

Thank you for reaching out and sharing your perspective.

As a global company, we follow the laws and regulations everywhere we do business.

While we explicitly prohibit illegal activity on our network, we are equally committed to protecting legal commerce. If a transaction is legal, our policy is to process the transaction. We do not make moral judgments on legal purchases made by consumers.

Visa does not moderate content sold by merchants, nor do we have visibility into the specific goods or services sold when we process a transaction. When a legally operating merchant faces an elevated risk of illegal activity, we require enhanced safeguards for the banks supporting those merchants.

For more information on Visa's policies, please visit our network integrity page on Visa.com.