IANAL, but if the page is used to opt-out of marketing emails, then yes, Visa is in violation the US CAN-SPAM act, which requires promptly processing opt-out requests.
As long as the opt-out page is broken, they should not be sending out marketing emails and could be open to a class-action lawsuit from people they email with no ability to opt-out.
https://www.ftc.gov/business-guidance/resources/can-spam-act...
As long as the opt-out page is broken, they should not be sending out marketing emails and could be open to a class-action lawsuit from people they email with no ability to opt-out.