Jesus formed one Church, and He sent the Holy Spirit to lead and guide her into all the Truth. The enemies of His Church have to try to justify their “not-religion” denomination - with their deletions and false additions to His Truth - thus they claim - they assert that they are right. If the Church is right, then they are gravely wrong and in big trouble - hence anything “Catholic” MUST be wrong. It is a pathetic argument composed by simply claiming they are right.
You might ask when, exactly, did their man-made theology get “revealed” to the world (when, in other words, was their church or non-church founded)? If they can give a date, ask them what happened to the Gospel from the time His One Church was founded by Jesus Christ, and the time this “new” gospel got here. Jesus did say, “Lo, I am with you until the close of the age.” (Notice the age still has not closed…)