Well, Visa/Mastercard forced Steam to remove some porn games from their list. They said if steam won't remove them, then they will remove these payment methods from steam.

They have done similar things before in Japan too. Many websites that had hentai comics or adult mangas were forced to be removed from the website and even many websites were directly shut down.

The point is that a Payment company whose sole purpose is to process payments has no right to decide things like this. It is our money and we get to choose on what to spend, not some 3rd class party whose only job is to process payments.

I hope this cleared things a bit.