Valves statement also matches with the claims of Itch.io, Stripe, and what Collective Shout themselves have claimed. So we've got two different claims, on one side are Visa and Mastercard, and on the other we've got literally everyone else. I feel pretty confident about which one is a load of bullshit.

It's also worth noting that Visa and Mastercard are playing semantic games with their statements. Nobody ever claimed they were "refusing legal transactions", rather what they're doing is threatening to stop working with any business that doesn't implement censorship that they're happy with. It's a subtle but important difference and they've never denied that's what they're doing.

Edit: rereading Mastercards statement they are claiming they don't restrict how businesses operate (although they do weasel around a little bit about illegal content), although Visa still hasn't denied that. They may also be playing games with that statement because porn is illegal in some countries that Mastercard operates in so they may be trying to claim porn is an illegal transaction despite businesses not selling it in the countries it's illegal in.

Edit 2: It just occurred to me this could also be about the UK and some US states new (and horrible) porn ID laws. I'm not aware of Valve doing anything to implement the strict age verification those laws are requiring for sites that distribute porn, and Visa/Mastercard could be trying to argue that without that in place any porn games Valve sells are "illegal transactions". In theory Steam does have age gating, but it's the same "are you over 18?" easily bypassed check that porn sites have always used.

both because they’re not responsible for this shit show

Nobody is forcing them to use mastercard and visa services