My reformed church is also filled with ex RC’s
"We ought to remain in the Church that was founded by the Apostles and continues to this day. If ever you hear of any that are called Christians taking their name not from the Lord Jesus Christ, but from some other, for instance, Marcionites, Valentinians … you may be sure that you have not the Church of Christ there, but the synagogue of Antichrist. For the fact that they took rise after the foundation of the Church is proof that they are those whose coming the Apostle foretold. And let them not flatter themselves if they think they have scriptural authority for their assertions, since the devil himself quoted Scripture, and the essence of the Scriptures is not the letter, but the meaning. Otherwise, if we follow the letter, we too can concoct a new dogma and assert that such persons as wear shoes and have two coats must not be received in the Church."
St. Jerome (342-420AD)