When it comes to creationism, the guiding principle of subsidiarity applies. Subsidiarity is the organizing principle within Catholicism. It states that matters ought to be handled by the smallest, lowest or least centralized competent authority. In particular, political decisions should be taken at a local level if possible, rather than by a central authority, but in general all decisions should be taken at the most local level which still resolves the problem.
So, here's the problem.
Experimental science was invented by the Catholic Church. There has been no lack of good Catholic scientists, centuries and centuries of them, who would have been happy to demonstrate that the Bible is a good experimental science textbook - if that were true.
But, they were GOOD CATHOLIC scientists, who followed the evidence of natural revelation and came to the conclusion that, even though the Bible gives us many examples of how to run a scientific experiment, it is not actually any good as a science textbook. They tried to show it for centuries. But, as Galileo and Cardinal Bellarmine (a doctor of the Church) both agreed, the Bible tells us how to go to heaven. It does not tell us how the heavens go.
The Catholic scientists who invented experimental science, who showed the world how to do experimental science, these are the men who tell us the Bible cannot be used that way.
Following the principle of subsidiarity, and the clear evidence of my senses that these gentlemen know what they are talking about - for I have benefited from their knowledge of the natural world in the physical comfort these generations of Catholic scientists have given my family and myself - I am not going to second-guess them. The Church says the Bible is not a science textbook, the Catholic scientists say the Bible is not a science textbook, and I believe both of them.
So, I reject Creationism.
Why Creationism is DangerousIndeed, I would argue that the Creationists are the major drivers behind atheism and have been for centuries. As St. Augustine pointed out nearly two millennia ago:
"Usually, even a non-Christian knows something about the earth, the heavens, and the other elements of this world, about the motion and orbit of the stars and even their size and relative positions, about the predictable eclipses of the sun and moon, the cycles of the years and the seasons, about the kinds of animals, shrubs, stones, and so forth, and this knowledge he holds to as being certain from reason and experience. Now, it is a disgraceful and dangerous thing for an infidel to hear a Christian, presumably giving the meaning of Holy Scripture, talking nonsense on these topics; and we should take all means to prevent such an embarrassing situation, in which people show up vast ignorance in a Christian and laugh it to scorn.
The shame is not so much that an ignorant individual is derided, but that people outside the household of faith think our sacred writers held such opinions, and, to the great loss of those for whose salvation we toil, the writers of our Scripture are criticized and rejected as unlearned men. If they find a Christian mistaken in a field which they themselves know well and hear him maintaining his foolish opinions about our books, how are they going to believe those books in matters concerning the resurrection of the dead, the hope of eternal life, and the kingdom of heaven, when they think their pages are full of falsehoods and on facts which they themselves have learnt from experience and the light of reason?
Reckless and incompetent expounders of Holy Scripture bring untold trouble and sorrow on their wiser brethren when they are caught in one of their mischievous false opinions and are taken to task by those who are not bound by the authority of our sacred books. For then, to defend their utterly foolish and obviously untrue statements, they will try to call upon Holy Scripture for proof and even recite from memory many passages which they think support their position, although they understand neither what they say nor the things about which they make assertion. "
-- Augustine of Hippo, The Literal Meaning of Genesis. vol. 1, Ancient Christian Writers., vol. 41, Translated and annotated by John Hammond Taylor, S.J. New York: Paulist Press, 1982That is, by insisting the something is Catholic doctrine when it definitely is not, Creationists have brought into doubt points of Catholic doctrine that the Church actually DOES teach. Their refusal to accept subsidiarity, their refusal to submit to the authority of natural revelation ("the heavens are telling the glory of God") is a model of disobedience. Creationists refuse the authority of natural revelation, so those who study natural revelation refuse the authority of supernatural revelation (the prophets, the apostles and Christ Himself).
Catholics embrace "both-and". Truth cannot contradict truth. Both natural AND supernatural revelation are true. But creationists force men into a duality, "Accept our understanding of supernatural revelation OR accept natural revelation, but you can't have both!" Worse, by claiming to judge those who actually do study natural revelation, the creationist claims a level of expertise in regards to natural revelation that they really do not have. When creationists mis-represent or misunderstand the natural world, is it really much of a leap for someone to conclude that they also cannot be trusted to correctly represent supernatural revelation?
As the priest, bishop, Father and Doctor of the Church, St. Augustine, noted above, this is not a recipe for success.
What does the Church Teach?
Catholic teaching is on faith and morals. Experimental science describes the mathematical, quantitative relationship between objects. Catholic theology describes the quality of the relationships between persons, human, angelic and divine. Quantity vs. quality. Objects vs. persons. These are two different areas of expertise.
What, exactly, is "faith and morals"?
"Faith" is about the trust relationship between persons, how one person can have trust in another person. If I have faith in you, then I trust you to do something, because I know you. Faith requires evidence. It is based on the evidence of my past interactions with you. Faith is not blind, it REQUIRES evidence.
So, in Christianity, "faith" is a shorthand way of asking the following questions: "Does God exist? if He does, Who is He?"
Put yet another way, "faith" is the same as asking "What evidence do I have to show that He exists and/or Who He is and what characteristics does He possess?"
"Morals" is likewise just a shorthand way of asking, "If He exists, do I relate to Him at all, and if so, how do I relate to Him?"
So, faith answers the question "Do I trust Him?" and morals answers the question "How do I relate to Him?"
In order for Young Earth creationism to be part of God's self-revelation in faith or morals, that is, in order for creationism to be integral to Catholic teaching, then creationism would have to tell us something about Who God is or how we relate to Him that can be known in no other way. Further, what creationism tells us about God would have to be non-contradictory with the other aspects of God's self-revelation.
But creationism doesn't do any of these things.
Thus, creationism is not a part of either faith or morals.
What creationism DOES tell us - God created everything, and He loved us into existence - can be equally told to us via evolution and the Big Bang theory. Creationism doesn't really say anything special.
Creationism might be true - Catholics are not forbidden from being creationists if they really believe that's where the evidence leads - but, since it isn't part of faith and morals, Catholics are not bound to believe it, and most post-industrial Catholics who have looked at it don't buy it. That said, a lot of pre-1900s Catholics did buy into creationism. But that isn't relevant to the Catholic Faith.
Pre-1900s Catholics believed a lot of things about the natural world that turned out to be incorrect. Priests, bishops, popes, doctors of the Church, even saints, had wrong theories about human conception (they did not know about the human egg), human nutrition (they did not know about vitamins), germ theory (did not know about cells), etc. Their wrong theories on these subjects are not part of faith and morals any more than creationism is. Pointing to their wrong theories in order to buttress creationist assertions is pointless at best, deliberately misleading and wrong at worst.
St. Augustine had the right of it.
Would that we followed his advice.