The Catholic Church is the Only True Church

It seems that many in the Church have accepted the notion that all people are going to Heaven.  That makes it rather unnecessary to join the Catholic Church, and indeed it doesn’t matter how you behave.  We are going to spend some time on this earth, and then we’ll go to our reward, where we’ll meet Napoleon, Pol Pot, Stalin, Ho Chi-minh, Henry VIII and Chairman Mao.
So many of the modern jingles that masquerade for hymns these days assume that we’ll all be OK in the end.  And some bishops go as far as to openly propose that we have little to worry about.
https://www.catholicnewsagency.com/column/how-many-are-saved-2383

The saints disagree, but what did they know?  http://www.olrl.org/snt_docs/fewness.shtml
So the trend today is to claim that the Catholic Church is not necessary for salvation.
The Catholic Church was founded by Christ Himself, Who declared: “I am with you all days, even to the consummation of the world" (Matt. 28:20).
All other Christian organisations have sprung from this original Church.  Around 40 000 of them.  Since they disagree with each other as well as with the Catholic Church, they cannot all be right.  Just one Church can be right.
In 2 000 years the Catholic Church has never reversed or repudiated any item of dogma.  This situation will continue until Christ returns.  The Pope, acting as head of the Church, binding all Catholics, can speak infallibly on faith and morals.
The Catholic Church has declared that outside the Church no one can be saved, on three occasions: Pope Eugene IV, Cantate Domino, 1441; Pope Innocent III, Fourth Lateran Council, 1215; Pope Boniface VIII, Unam Sanctam, 1302.
The saints agree.  Saints Irenaeus, Augustine, Alphonsus, Thomas Aquinas, Louis de Montfort, John Vianney, Francis of Assisi, Robert Bellarmine and others. 
So we can say that there is no Protestant in Heaven.  No Buddhist.  No Hindu, no Muslim, no atheist. But there may well be many ex-Buddhists, ex-Hindus, etc.
Does this mean that the overwhelming majority of the world population is damned?  Perhaps, perhaps not.  Protestant are baptised.  Their baptism is not a Protestant sacrament.  It is Catholic.  So Protestant children are baptised Catholics, in the state of grace, which remains until they commit a mortal sin.
All people who are baptised become Catholic.  Apart from baptism of water, there is baptism of desire, where those who genuinely seek Christ, even without knowing His Name, are baptised.  And there is baptism of blood, where a non-Catholic is baptised by martyrdom.
If we pretend that the Catholic Church is not necessary for salvation, we lose all incentive to win souls for Christ.  And given that Our Lady at Fatima told us that there are many who go to Hell because there is no one to pray for them, this lack of interest in bringing the faith to others might result in the loss of many souls.  And this abandonment of souls will be a topic for discussion at the judgement of those who teach falsely that all are saved.
If the Catholic Faith is not necessary for salvation, then the martyrs died horrible deaths for no reason at all.  We need to take an interest in saving others.  In doing so we might be able to save our own souls.