There is the sin of presumption — the belief that death will surely take me to my rightful place in paradise. There is also a philosophy of presumption — the belief that everyone has a right to eternal life unless they do something drastically bad to blow it.
However, there is no right to eternal life. As sinful creatures, there is no natural way we can enter into paradise because entering paradise means sharing in the life of the Trinity. God would be denying his own nature if he admitted to Trinitarian life any creature who was not permeated with eternal life.
The issue we face in life is not that Catholic teaching supposedly excludes people of other faiths from entering God's kingdom. The real issue is how anyone, good or bad, Christian or non-Christian, can receive eternal life. No one deserves or earns heaven; it is a gift of immeasurable magnitude.
To make it a possibility, however, the Son of God became human and with every breath of his life and in his death said "yes" to the Father. For a mere mortal to share in the life of God, his or her life must be conformed to the pattern of Christ's eternal "yes." We must say "yes" to Christ and, in particular, "yes" to the paschal mystery of his passion, death and resurrection. We must unite ourselves with his sacrifice on the cross.
This is not only the act of an individual. Rather, we are saved because we are incorporated into Christ's Body. That Body has a real material existence in the Church.
We are incorporated into Christ's Body through Baptism. We participate most profoundly in the Body of Christ through the Eucharist. The Eucharist is the memorial of the paschal mystery and the place where we unite our sacrifices with that of Christ. Indeed, each of the sacraments provides a bodily means of sharing in the paschal mystery.
The way to union with God is through a life of faith in Jesus Christ. We live that faith through personal prayer, participation in the corporate worship of the Body of Christ and by living in faith the events of daily life.
Is this an exclusionary teaching? No, it is beyond human fathoming that anyone can share in eternal life. Does this teaching mean that only Christians can receive eternal life? No, not necessarily. All we know is that eternal life must mean sharing in Christ's death and resurrection. Perhaps there are ways other than the Church and the sacraments through which God brings people into sharing in his very nature. But God has not revealed those ways to humanity.
The necessity to evangelize and bring the Christian faith to others is a serious responsibility. But the mercy of God is also real. God doesn't make junk. Every bit of creation has an eternal destiny. How that destiny will unfold is, in this world, far more than we can understand.