Besides the many arguments against the Protestant concept of Sola Scriptura from history, Scripture and logic, I think we could posit another fourth category of objections based on the subjective dispositions such a doctrine brings about in those who adhere to it. It is my contention that the Protestant doctrine of Sola Scriptura leads to a prideful disposition in the soul, which is forced by logical necessity to invest its own opinions with the authority of divine revelation. The Catholic teaching of an authoritative Church that hands on doctrine, however, leads the soul to humility and docility, for the doctrine is received as a gift given gratuitously. Let us examine this further.
Catholics and Protestants come at the truth through two different avenues. In Catholic theology, we look at the content of Divine Revelation and interpret it through the lens of our own tradition, which we hold to be authoritative. Thus, while certain questions are open for discussion, there are many others which we hold as "settled."
Thus, in Catholicism, truth is something that is given. It is a gift. In the first place, a gift from God, who gives us revelation gratuitously for the sake of our salvation, but secondly, a gift from the Church itself. Nobody learns the faith on their own; it is handed on from generation to generation, and the essence of what it means to be Catholic is to receive this truth humbly and with docility. Thus, the Catholic concept of Divine Revelation as being handed on and protected by the Church promotes an attitude of doctrinal humility even while allowing us to repose in the certainty of the content of those doctrines. Doctrine is primarily something that is received.
This is an interesting contrast to Protestantism. In Protestantism, there is no idea of an absolutely authoritative tradition. Some Protestant groups value tradition more than others, but no Protestant sect teaches that any tradition can have divine authority behind it, as we do. Thus, all authority, ultimately, must rest with the individual, who decides for himself what is truth and what is error. He may consult tradition, or the teachings of others wiser and older than himself, but ultimately it is the believer and the believer alone who decides how much influence he will allow these teachings to have. Doctrine is not something that is given and received in humility, but something that each person must painstakingly sort out for themselves.
If doctrine is not something that is given, then it is not something that is received. It is something the believer kind of cobbles together, based on whatever criteria he wants to include or not include. In Protestantism, all doctrine is ultimately the creation of the believer. As such, the believer always has what we could call a "vested interest" in defending his doctrines because they are really his in a way that doesn't apply to the Catholic, whose teaching is handed on and received.
This means that, for a Protestant, defending his doctrine means defending his own privately formed opinions. They might be opinions shared by a great many other Protestants, but they are still opinions, because there is no final arbitrating authority in Protestantism other than a fuzzy consensus. Note the difference between Catholicism and Protestantism here - in the one case, believers are empowered to adhere to certain, infallible truth but in a spirit of humility, which is possible because the doctrine of the Catholic is now his own. On the other hand, the Protestant, who has no infallible authority beyond himself, is forced to make a "personal investment" in his own doctrine. His own doctrine represents his common sense, spirituality and personal judgment all wrapped up into one. Thus, for a Protestant, it would seem that it is much more difficult to have that sense of humility and awe before the truth that is so necessary for spiritual growth.
How can one be humble and docile before a truth that one ultimately does not receive but creates? I am not accusing all Protestants of being prideful, but it seems that the manner in which Protestantism teaches that doctrine should be appropriated leads rather to pride in one's own judgment and opinions than to humility. Is dogma a gift handed on or is it our own fabrication? If it is a gift, we can repose in wonder and humility before it; if it is a creation (which it ultimately must be if we reject authoritative tradition), then it comes with all of the arrogance and close-mindedness that all men display when defending their own personal opinions.
Interesting how we could apply this principle to liturgy, too (liturgy that is handed on versus fabricated and which promotes a greater sense of humility - are we the humble recipient or the grand master?).
John 7:16~ "Jesus answered them, and said: My doctrine is not mine, but his that sent me."