You mean infalllbly, or what level of magisterial teaching (encyclical, etc.) has forbidden it?
And are all methods of interrogation endorsed by the prosecutorial profession today, and should former Catholics be prosecuted in some way, and what kind of interaction can lay have with them?
Former Catholics are vy that very fact in a state of sin that they need to wash away by confession and repentance, as well as any other unconfessed sin they accumulated on their conscience while away from the Church. Unless they publicly profess Catholicism, yet teach Protestantism (or any other falsity), they are not a subject for the Holy Inquisition, however, which is concerned with the state of Catholic priests primarily and Catholic lay teachers secondarily.