Valve confirms credit card companies pressured it to delist certain adult games

Simulated "immoral" activity could be considered a moral gray area. If nothing else, morality is subjective.

So I think it's reasonable to argue for private, individual consumption of morally subjective material (not least of which is the logistical difficulty of preventing such things), as well as the right to create and sell such things. (You or I might approve of or oppose those things, but that's a different argument from what I make below.)

Aside from that, I don't think Valve or a payment processor is obligated to be a neutral party. Whether it might come from collective consumer backlash or whoever makes decisions for an organization deciding what they will or will not allow to flow through their system, I think they too should have the right to allow or ban things. If publishers and consumers want their morally gray content, so be it, but don't feel entitled to have Steam and VISA along for the ride if they don't want to be.

Hypothetically, Valve might prefer Steam be neutral, because money. But then they have the option to fight their payment processor or look for alternatives, rather than "forcing" their payment processor to be a part of something that the payment processor opposes.

TL;DR when a morally subjective issue involves a lot of parties, every party should have the right to "opt out" if they are morally opposed. (in my opinion)

Payment processors banning companies from using them for anything other than illegal use or fraud issues seems like pretty egregious overreach to me.

They shouldn't be able to leverage their nigh monopoly on modern payment processing to choose winners and losers in the marketplace.

They are using pornography as a wedge issue to establish that they get to dictate what companies are allowed to exist in the modern distributed market.

It would be entirely reasonable to legally require them to act blindly towards retailers, with restrictions needing to be based on universally applied financial criteria.

Card payments have become inseparable from modern life.

Regulate them as a financial utility. The electric company or water company can't refuse to hook up a business just because the owner doesn't like that business.

I think the trouble here stems from the lack of alternatives to the small group of payment processors. The near-monopoly allows their choices to override the choice of all the other involved groups, and almost no viable alternatives exist for Valve to move to if they disagree.