Reading the bible is hard. It is a very old book, so much of what is written in there can be difficult to interpret. Who knows what figures of speech have been lost to time. Add to that the fact that it has to be translated into our language, and the possibility of misreading the real intent of the text becomes fairly high. When a Christian comes across a passage that seriously challenges their preconceptions, their first instinct is often that their understanding of the passage must be wrong. To determine that their understanding is indeed wrong takes a lot of work, and often they will simply assume that such work would yield answers and simply move on without giving it a second thought. This seems like a terrible thing.
But in the interest of fairness I tried to come up with an analogous situation for me to come across. The best example I can think of is in the realm of quantum mechanics. There are a lot of things in quantum mechanics that are really counter-intuitive. It is quite possible that I could read a fact about quantum mechanics which doesn't sound right to me. I would assume that I am most likely wrong and my knowledge of quantum mechanics is lacking. Chances are that I would not go to the trouble to learn enough about quantum mechanics to fix these gaps in my knowledge, I would simply assume that such a search would lead to an answer and be on my merry way. I don't really think anyone would begrudge me for this.
Am I being unreasonable to the Christian, or is there a significant difference in these 2 situations? The more I think about it, the more I think the problem here is that I haven't given enough information. One the surface, it seems that these 2 situations are the same and show that I am being unfair, but I think if we add more details to make 2 people more analogous, and the expectations of them will turn out roughly the same.
I think a key factor is how the Christian came across the confusing verse. If someone (perhaps an atheist like myself) approaches them and shows them the verse out of the blue, I think it would be reasonable for the Christian to just shrug it off and assume that an experienced theologian would have an answer. This situation feel analogous to a random person like myself coming across a confusing fact about quantum mechanics and just moving on with their life. If either person gets curious and pursues the matter further, great. But I don't think they should be expected to follow every confusing thing they come across in life, our time is limited after all.
On the other hand, if the Christian came across the verse reading the bible on their own, or perhaps during a bible study, I think it would be somewhat reasonable to expect them to reflect on the problem and try to find a real answer. If they are doing these things, they are presumably trying to better their understand of the bible and their religion. I think it would be somewhat disingenuous of them to continue on 'studying' other parts of the bible when they have already come across an interesting item and they have ignored it. This seems analogous to a physics student who comes across a difficult section in their textbook which they don't understand, and instead of going to the trouble to figure out the details, they just turn the page and keep on going with the next section. I think we can all agree that this is a description of a bad student.
The last group that I want to think about is any Christian who is trying to "spread the word". These are people who are out actively trying to get people to convert to Christianity, and honestly probably the group of people I was thinking about in my first paragraph. For them, I think it is reasonable to expect that they actually have an answer (or at least are willing to go out an seek an answer) for the troubling things that come up in the bible. It is simply not okay for this group to completely ignore difficulties with their religion and assume that other people have the answer that they don't. This would be analogous to me trying to go around and convince people that quantum mechanics is correct. If I were to take on a role as a teacher, you would definitely expect me to understand these details. Once again, we see that if we alter these two situations to make them truly comparable, there is no real difference in expectation.