If you have a doubt about the teaching of the Church, and decide to read materials that are an apologetic against the Church’s teaching with which you are struggling, is that sinful?
Contrary to what others have said, yes, it is.
Your first obligation is to (a) find out precisely what the teaching is and (b) find out the rationale behind it. The Church does not arbitrarily create doctrines because she finds the whole experience exhilarating. She does so because, through a specific order of reasoning that has been guided by the Holy Spirit, she has arrived at that truth. Our obligation as lay people is to understand that reasoning while exercising the virtue of piety, which is the proper honor due to those in authority over us.
Does this mean we may never read books that are apologetics against the faith? No. It means that we should not do so without sincere necessity and while exercising prudence without overestimating our own education. Don’t give in to mere curiosity, which is the vice of having an unmoderated desire for knowledge beyond your state in life. If you are not a scholar, don’t lust after the knowledge of scholars.
Now, inevitably, the modern person will say, “Oh, that’s so anti-intellectual! I prefer to be scholarly and objective. This sounds so biased.”
This is a wonderful appeal to the narcissism of our age, where anyone who can Google is suddenly a free-thinking intellectual. But this assumes that the average individual has even one-tenth of the necessary education to address certain fundamental aspects of philosophy or theology in a sincerely objective and sincerely scholarly manner.
The vast majority of us simply read books that are either popular-level or simply out and out polemics. About whatever perspective we should desire to learn more about. The vast majority of us simply do not have the ability, lack the formation, to do anything more than that. For us, our education happens to be rooted in the particular books we’ve chosen to read. And no one, absolutely no one, can acquire doctoral-level expertise in the dozens of requisite fields to TRULY be objective and TRULY be scholarly. There is no thinker out there who has absolutely exhausted human knowledge and has arrived at the most intellectually sound position possible. We have all stopped where we thought the evidence has sufficiently proved our case to a probable degree. That includes the many who wear a social mask of atheism, where they can exalt their own intellect without revealing the thousands and thousands of limitations they’re constrained by.
So we all are in the same boat. But the Catholic, indeed, does not believe that faith is wrangled out of the hands of a scholar or out of a book. We don’t believe in some sort of intellectual yoga wherein we can position ourselves in just the right manner to see things as they really are.
No. God grants us the ability to say yes to divine revelation, lest any man should boast in his own intellect, or claims that he has, all on his own, wrestled truth out of God. That ability is called faith, and without it, we can only have a human opinion.