The card itself may have contained other security features such as a holosticker or a serial number in human readable form. Inspection is more than just scanning an RFID. It's the transit authority's ticket - they can set the rules about how you use it. The breaking the law bit, in the UK at least, comes from the railway by-laws incorporated into the Transport Act 2000 - being on railway premises in a compulsory ticket area without a valid ticket. In the UK a ticket bought with a discount, using an annual Gold Card for example, is only valid with the associated photo ID; even if you've paid the fare if you forget the Gold Card & ID, the ticket's not valid.