I have often seen a quotation attributed to Mohandas Gandhi. "I like your Christ, but I do not like your Christians," or some variant on it. Now, he probably didn't say it as such. The closest possible source of this paraphrase is the 1925 book The Christ of the Indian Road by E. Stanley Jones, who apparently was a Protestant pastor serving in India, and it seems to be something consistent with Gandhi's thought at any rate.
So what's the problem? Humans are social animals, and we are called to communion with one another. We cannot exist independently. Faith comes from what is heard as we learn in the Scriptures. In the normal context of things, this indeed comes from the teachings provided by other people.
That being said, our encounter with the Lord is profoundly personal. Jesus Christ died on the Cross not simply for our sins, but for us. Each of us. Every unique and unrepeatable being. Jesus Christ is the meaning of the world and of our lives, and each of us must step outside of ourselves to recognize this in the individual cooperation of grace with human freedom.
As we understand our call to be with one another and that Faith comes from others before us, we must realize that people are only perfected in Heaven, after striving for it through living the life of the theological virtues of Faith, Hope, and Charity.
We talked about this in theology class this past semester in our discussions on the Catholic Church as the Church of Christ and the question of Extra ecclesiam nulla salus. Only God is aware of the reality of anyone's interior life, and so only He has the understanding of one's relationship to the Catholic Church, whether it be perfect or imperfect communion (through Protestant baptism usually). That also means only He knows of implicit faith, which brings us back to the Gandhi problem. We Christians are often asked about people like Gandhi and their salvation. They were good people, I am told, so what about their salvation? Surely God would not send them to Hell. First and foremost, "Stop playing God," as Fr. Leger says. We cannot think like God, so don't!
Secondly, the Church is a hospital for sinners, and we have to recognize it. The Church is perfect as she was instituted by Christ, as His earthly instrument to sanctify souls and His eternal communion with us in Him. Implicit faith requires that one accept the Gospel provided it is presented effectively while holding on to it in a way possible while in ignorance of the Gospel still. What does "effectively" mean? Good question, one for God actually. He alone knows if one's rejection is formed through some defect of reason not of the person's own making or whether it was of one's unimpeded will.
That means to judge Christians based on their failings and thus rejecting Christianity, and specifically the Holy, Catholic, and Apostolic Church, as holding the Truth in full is quite a perilous act. Thus Venerable Fulton Sheen's words.
On a somewhat related note, my friend has pointed out numerous times that it must be awful to be a Protestant who accepts salvation sola fide, since there are no canonized saints to serve as specifically chosen examples of the Christian witness, living lives of heroic virtue through cooperation with grace and turning the ordinary into the extraordinary. Your parents and good aunts and uncles are one's closest reference point for standards of good human beings, and that's just about it. Maybe a famous politician like Nelson Mandela can be thrown in there too, but that's it, and when one has only a vague idea of holiness or a fuzzy concept of good, these examples can be pretty useless in the end.