Alice von Hildebrand wrote recently about this issue: There's entirely too much focus on "salvation" when talking about the Church/churches. Our primary purpose ON EARTH is to glorify God. We do that by knowing, loving, and serving God through the fulfillment of our duties. We can do that only if we know the truth about God and about ourselves.
The Catholic Church has NEVER taught that only registered Catholics are saved. What the Catholic Church DOES teach is that those whose knowledge of God is partial, or whose knowledge of how God wants us to serve Him is partial, or whose knowledge of what is truly good for human nature is distorted, cannot glorify God as He truly deserves.
THIS is sufficient reason to spread the gospel and engage in missionary activity. The Universal Call to Holiness cannot be properly answered by those who have only part of the truth and part of the means of grace--i.e., ALL of the sacraments.
It is NOT true that, if one admits that non-Catholics or even the unbaptized, can be SAVED, then all motivation for spreading the gospel collapses.
That is what the Feeneyites constantly proclaim. It is part of their heresy--this exclusive focus on SALVATION, that makes Feeneyism a form of Protestantism.
In the 1930s and early 1940s Fr. Leonard Feeney (1897-1978) was known to the public mainly as a writer of better-than-average poetry and of popular books such as "Fish on Friday." From the late 1940s until his death he was known instead for his rigorist interpretation of the maxim "extra ecclesiam nulla salus" ("no salvation outside the Church"). Adherents to his interpretation became known as "Feeneyites."
Ordered to stop teaching his interpretation, Feeney refused and was excommunicated, not technically for teaching heresy but for disobedience. He was reconciled to the Church before his death, and the excommunication was lifted. Some of his followers have tried to construe the reconciliation as a Vatican affirmation of Feeney's theology, but, since the excommunication did not extend beyond a matter of obedience, the lifting of it did not extend any further.
Catholic Answers
His teaching was not heretical. His refusal to "keep it quiet" was the reason for his excommunication.