Conveniently using separate quotes out of context to prove the mistaken position does not work. Take for example Pius IX:
Pius IX, Quanto Conficiamur Moerore, 1863 said:
There are, of course, those who are struggling with invincible ignorance about our most holy religion. Sincerely observing the natural law and its precepts inscribed by God on all hearts and ready to obey God, they live honest lives and are able to attain eternal life by the efficacious virtue of divine light and grace. Because God knows, searches and clearly understands the minds, hearts, thoughts, and nature of all, his supreme kindness and clemency do not permit anyone at all who is not guilty of deliberate sin to suffer eternal punishments.
You quote the paragraph that may be misunderstood in your favor and leave the rest of the piece out!
Here is the rest of the paragraph:
Here, too, our beloved sons and venerable brothers, it is again necessary to mention and censure a very grave error entrapping some Catholics who believe that it is possible to arrive at eternal salvation although living in error and alienated from the true faith and Catholic unity. Such belief is certainly opposed to Catholic teaching. There are, of course, those who are struggling with invincible ignorance about our most holy religion. Sincerely observing the natural law and its precepts inscribed by God on all hearts and ready to obey God, they live honest lives and are able to attain eternal life by the efficacious virtue of divine light and grace. Because God knows, searches and clearly understands the minds, hearts, thoughts, and nature of all, his supreme kindness and clemency do not permit anyone at all who is not guilty of deliberate sin to suffer eternal punishments.
And then he goes on saying:...
Also well known is the Catholic teaching that no one can be saved outside the Catholic Church. Eternal salvation cannot be obtained by those who oppose the authority and statements of the same Church and are stubbornly separated from the unity of the Church and also from the successor of Peter, the Roman Pontiff, to whom "the custody of the vineyard has been committed by the Savior."[4] The words of Christ are clear enough: "If he refuses to listen even to the Church, let him be to you a Gentile and a tax collector;"[5] "He who hears you hears me, and he who rejects you, rejects me, and he who rejects me, rejects him who sent me;"[6] "He who does not believe will be condemned;"[7] "He who does not believe is already condemned;"[8] "He who is not with me is against me, and he who does not gather with me scatters."[9] The Apostle Paul says that such persons are "perverted and self-condemned;"[10] the Prince of the Apostles calls them "false teachers . . . who will secretly bring in destructive heresies, even denying the Master. . . bringing upon themselves swift destruction."
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He said that God in His mercy will not forget those who are struggling with invincible ignorance. God will ensure that these souls that sincerely ask and seek, will join the Catholic Church before death so those of good willed will not perish.
Also, was not this same Pope IX who later on wrote the "Syllabus of Modern Errors" in which indifferentism is definitely condemned, perhaps because he was aware of how the liberals wanted to twist his words and allow salvation for Non-Catholics? Take a look at these four condemned errors:
15. Every man is free to embrace and profess that religion which, guided by the light of reason, he shall consider true. -- Allocution "Maxima quidem," June 9, 1862; Damnatio "Multiplices inter," June 10, 1851.
16. Man may, in the observance of any religion whatever, find the way of eternal salvation, and arrive at eternal salvation. -- Encyclical "Qui pluribus," Nov. 9, 1846.
17. Good hope at least is to be entertained of the eternal salvation of all those who are not at all in the true Church of Christ. -- Encyclical "Quanto conficiamur," Aug. 10, 1863, etc.
18. Protestantism is nothing more than another form of the same true Christian religion, in which form it is given to please God equally as in the Catholic Church. -- Encyclical "Noscitis," Dec. 8, 1849.