Indeed! Though it's important to note that it's more than just that (as important as age verification of performers is!).
Mastercard and Visa are also acting as de facto controllers of what is acceptable content. In other words, not just who is participating, but what is being done.
For example, "… blood is banned, even blood obviously made of ketchup. This is a disaster for vampire porn, which is akin to a forbidden good on the internet." That's not my thing, but I also don't think Mastercard and Visa should be the ones who regulate that.