Many atheist seem to believe that undermining Christianity begins with making an argument against the existence of God. However, I think this approach mostly demonstrates that people are forgetting something else that is important to Christianity, namely faith. While doctrines, rituals, churches, and moral practices are important to Christians, faith seems to be the most fundamental part of it. You can believe in the doctrines, practice the rituals, and go to churches but not have faith. What is faith? While many Christians profess to understand "faith", I think many of them get it wrong. The reason why I think they get it wrong is that they tend to use a common argument for faith, it goes like this:
Suppose that you are going to take a trip to another country through an airplane, but you have no idea what the exact risks are. You don't know that you might even make it safe to the other side, since it is possible that things can go wrong for you: bad weather, terrorism, professional incompetence, etc. Nonetheless, you still used the airplane anyways, since you believe that you will be safe. On the surface, this seems to describe what faith is. A lot of people may agree that this is basically the nature of faith. However, I want to contend that this is an incomplete account of faith. The problem with this argument (or illustration that serves to make an argumentative point) is that it provides a deflationary account of faith: all faith is, is just making an assumption. The illustration being deflationary alone is not what makes it wrong, rather it is simply wrong because it fails to consider another element of faith. This is the say that having faith does involve making assumption, so the illustration is not completely wrong. However, it is incomplete since it does not consider the important element of faith which is having unconditional commitment or
unconditional conviction that something is true. To have this unconditional commitment and conviction means to believe in something no matter what, it is to assume that something is true without evidence even if it is contrary to all considered judgment and evidence. When this element is taken into consideration, it becomes apparent that there is a difference between merely believing (or assuming) something and having an unconditional commitment that what you believe must be true no matter what our all-considered judgment tells us.
Merely believing in something can be conditional, you can believe in X but eventually give up believing in X. You can concede that believing in X was wrong, given the all-considered-evidence. You can concede that at one time you did believe in X, but right now you no longer believe in X. Many times believing in something can be used as a "working-hypothesis", which you believe in but you use it to see if it best explains the environment around you or solves problems more efficiently. However, when it comes to the point when it stops being a plausible explanation or an efficient problem-solving tool, then you would have to either adjust it or replace it with something else. This is pretty acceptable, but when it comes to faith it seems to be the opposite: you can never abandon your beliefs even if the evidence says otherwise. Suppose that you are in a situation where you have to make a quick decision to save everybody, but you have insufficient information to base your decision on. You do not know which decision is the most well-informed kind, but you do not have the time to consider which decisions are best supported because people will die very soon. In such a situation, some people argue that you must make a "leap of faith". However, the problem with this is obvious, considering what I said earlier. There is a huge difference between merely believing that your decision was a wise one and having an unconditional commitment that it is the wise decision. The situation does not necessarily call for unconditional commitment to a quick-decision, it simply calls for a more efficient approach which is quickly deciding something based on knee-jerk intuitions. Suppose that you did make a quick decision, but everybody is killed. In such a case, you will admit that your decision was not a very good one, you will admit that what you believe to be a good decision was actually wrong. However, with faith it seems like in spite of contrary evidence (deaths of people), you will still believe that you made the right decision.
But what about Christians who stopped believing in the inerrancy of the bible and believe in evolution? I think the scope of unconditional commitment is different for every Christian, some Christians have the scope of unconditional commitment that is as wide as believing in the infallibility of the bible down to every statement and every doctrine of certain denomination. Others will have their scope limited to the basic fundamental beliefs such as resurrection, holy trinity, atonement, and divine inspiration, while all other beliefs are merely provisional beliefs that can change over-time such as creationism or historical accuracy of the bible. However, I think any kind of unconditional commitment is fundamentally wrong. I think all our commitments in regards to belief ought to be conditional on evidence.
Someone might ask me if my commitment to evidence is unconditional, my response would be that it is conditional. However, even if it were conditional, it does not follow that it is a weak belief. We can have conditional commitment to strong beliefs, but these conditional commitments presuppose a falliblism of beliefs; any belief is susceptible to be wrong. However, I think the problem with such kind of question is that it conflates justification with beliefs: not all beliefs are justification, such as evidence. Evidences are not beliefs, since beliefs are states of mind while evidences are independent of our minds (although they are interpreted by our minds). We depend on something on external reality, namely evidence, to justify our beliefs about reality; sometimes it agrees with it (to a degree), other times it does not.
However, I have not said exactly why I think faith is problematic. My ultimate problem with faith as unconditional commitment is that it eventually amounts to dogmatism. Many believers would disagree with me here, but I suspect that they disagree with me because when they think of dogmatism they have a certain picture in their mind such as extremism and fanaticism. However, this is not what I am saying. I am not saying that faith amounts to fanaticism, I said it amounts to dogmatism. Fanaticism is when unconditional commitment becomes dysfunctional and abusive to individuals and society; extremism is unconditional commitment to beliefs that can lead people to harm others. However, it is possible to be dogmatic without being a fanatic or an extremist (while all fanatics/extremists are dogmatic, not all people who are dogmatic are fanatics/extremists). You can unconditionally believe that there is a God without becoming a suicide bomber, but this unconditional commitment is still dogmatism. Dogmatism is not always harmful or immoral, but it is irrational. It is irrational because you are giving beliefs the kind of commitment that is disproportionate to what it actually deserves; all beliefs are susceptible to be false (this is what I call falliblism, which is not the same as skepticism), so none of the beliefs deserve unconditional commitment but rather conditional commitment. However, it comes with degrees; some beliefs are stronger than others because they are better supported, so we should have more commitment to those beliefs until it is shown that they are false (or unlikely).
To be dogmatic is simply unwilling to consider that your beliefs are false or untenable when there are reasons to think so. It is possible that we cannot know that your beliefs are false, but it is still untenable; it is not very well supported to the point that it does not deserve unconditional commitment. You should make unconditional commitment to things that we infallibly know to be true, but this almost never happens. We can almost never infallibly know something to be true. However, when your belief lacks support you shouldn't have unconditional commitment to that belief, you should simply refrain from making any kind of commitment to it.
When faith is out of the picture, the belief in the existence of God deserves conditional commitment (or no commitment at all). This means that at some point, we may have to abandon the belief in the existence of God when there are contrary evidence. However, it appears that most believers would not accept this at all: to them, there must be a God regardless of the evidence. They even go as far to say that science cannot tell us whether or not God exists. Nonetheless, I do not need to argue that science can disprove the existence of God (although I think science can show that it is unlikely), what I have to point out is that once faith is out of the picture the belief in God loses it's religious allure: the belief in God is simply just a belief like any other beliefs, but we are not required to have any commitments to believe in it because we do not have any evidence for it. Without faith, Christianity would appear incomplete and "half-assed".