There is but one Church founded by Christ, the Catholic Church. Historically, none other can trace their roots back to the time of Christ. For the first 1000 years of Christianity, if one was Christian, one was Catholic. There was no other Church. Then, in 1054 A.D., the Orthodox split off. They retained Apostolic Succession, and, therefore, all seven Sacraments. Only in 1517 A.D., did Protestantism begin. Now, there are literally thousands of man-made, doctrinally disagreeing denominations, all claiming to be led by the same Holy Spirit, reading the same Bible, but coming up with contradictory interpretations of the Bible. That cannot be the will of God. Nowhere does it say anyone was authorized to found a church or denomination apart from the Church built by Christ.
For any Protestant denomination to be “valid,” it would have to show 1) that the Catholic Church, founded by Christ failed and 2) show directly where Christ authorized anyone else to found a different Church apart from His. Also, if you can do 1, then we’re all wasting our time following Christ, because He failed, and therefore, is not God.
The Catholic Church is indefectibly holy, not because of the humans within it, but because it has Christ as its head and the Holy Spirit as its soul.
Jesus Christ had two natures when He was here on earth. One human and the other Divine. His human nature was like us in all things but sin. The Catholic Church, which St. Paul calls the Body of Christ, is similar. It has a human nature, composed of us humans, and a Divine nature, composed of Jesus and the Holy Spirit. The human nature of the Church, though, unlike Jesus, is sinful.
So, for any group to establish their church today and legitimately call it a "Christian" one, they MUST also hold to the first things, the common bond of the faith once delivered unto the saints. Where can someone find these? In Scripture, primarily, because it contains the direct revelation from God to the very men Jesus ordained to carry forth the truths He taught. The doctrines that ARE Christian are clearly spelled out in Scripture. Additional recourse is found in the writings of the early Christian leaders - though their word are not Divinely-inspired so they must be cross checked with Scripture. The early creeds are also helpful as are various commentaries, study Bibles and careful study of the origins of the faith. The so-called "Apostolic Succession" is one of a succession of the MESSAGE and not of the office of Apostle. All the Apostles discipled, taught, ordained and sent out additional leaders to preach and teach and to establish churches in new areas as souls were won to Christ. They had strict rules for who they okayed to do this and believers were warned constantly to test the spirits of those sent to them or who came presenting themselves as chosen leaders. If they did not teach what the Apostles taught, they were to be shunned and NOT followed. That's just how it was done back then. The "labels" were inconsequential to the teachings. You should already be aware - because it's been said many times - that the word "catholic" wasn't even used until the second century and was used to designate the universal faith as that which was always, everywhere and by all believed, and which was written of in Scripture.
This brings us to today. Can the Roman Catholic church legitimately claim to BE the church Jesus established? Is what they teach today the SAME thing that was taught to the first Christians by the Apostles? Perhaps some of the doctrines, but certainly not all of them. The Roman Catholic church today is every bit as man made as the denominations you criticize here. What makes a Christian assembly a genuine representative of the early church is the message and the behavior of its members. NO single denomination can claim to be the ONE and only church, because each one contains tares and wheat, believers and posers. Jesus' body WILL be made up of the wheat ONLY. It is His bride, made spotless by His precious blood, clothed in white robes washed in His blood, purified, sanctified and as righteous as He is righteous because it is HIS righteousness they are found in. Christ IS the head of this body and it IS already ONE. We are one in Christ REGARDLESS of what a shingle outside our church doors might say, and this is because of the gospel of the grace of God which gives to us eternal life through faith in Christ.
Why not make THAT your goal instead of provoking, goading, mocking and trashing fellow believers, brothers and sisters in Christ, just because they aren't in your church? To the glory of God!