That is the exact anticipated response and my reply will be that we are ALL still the same Church by virtue of John 3:16.
Scripture bears this out.
Matt. 12:25; Mark 3:25; Luke 11:17 - Jesus says a kingdom divided against itself is laid waste and will not stand. This describes Protestantism and the many thousands of denominations that continue to multiply each year.
Matt. 16:18 - Jesus says, "I will build my 'Church' (not churches)." There is only one Church built upon one Rock with one teaching authority, not many different denominations, built upon various pastoral opinions and suggestions.
John 10:16 - Jesus says there must only be one flock and one shepherd. This cannot mean many denominations and many pastors, all teaching different doctrines. Those outside the fold must be brought into the Church.
John 17:11,21,23 - Jesus prays that His followers may be perfectly one as He is one with the Father. Jesus' oneness with the Father is perfect. It can never be less. Thus, the oneness Jesus prays for cannot mean the varied divisions of Christianity that have resulted since the Protestant reformation. There is perfect oneness only in the Catholic Church.
John 17:9-26 - Jesus' prayer, of course, is perfectly effective, as evidenced by the miraculous unity of the Catholic Church during her 2,000 year history.
John 17:21 - Jesus states that the visible unity of the Church would be a sign that He was sent by God. This is an extremely important verse. Jesus tells us that the unity of the Church is what bears witness to Him and the reality of who He is and what He came to do for us. There is only one Church that is universally united, and that is the Catholic Church. Only the unity of the Catholic Church truly bears witness to the reality that Jesus Christ was sent by the Father.
Rom. 15:5 - Paul says that we as Christians must live in harmony with one another. But this can only happen if there is one Church with one body of faith. This can only happen by the charity of the Holy Spirit who dwells within the Church.
Rom. 16:17 - Paul warns us to avoid those who create dissensions and difficulties. This includes those who break away from the Church and create one denomination after another. We need to avoid their teaching, and bring them back into the one fold of Christ.
1 Cor. 1:10- Paul prays for no dissensions and disagreements among Christians, being of the same mind and the same judgment. How can Protestant pastors say that they are all of the same mind and the same judgment on matters of faith and morals?