Many atheists argue that they are being neutral by not believing in any deity. This neutrality is then turned into the basis for atheism being a "default position." Is this really a neutral position?

I have experienced this line of argument on many occasions.  Personally, I find it unreasonable.

Let's say you want to be neutral as possible when it comes to looking at religions.  How do we know what the "default position" is? What is the most reasonable "starting position" to start the journey of evaluating religions, or faith systems?  What can we know by mere intuition in regards to a faith system? (I say "faith system" because I think it's a stretch to call atheism and agnosticism religions, but I think it is reasonable to call them a type of faith.)

The first is basic reason and logic.  It is a simple truth that not all religions or faith systems can be true.  They contradict each other in many ways.  While there are generic similarities between most of them, such as believing in a higher power, being good, and affirming an after life, that does not make them compatible. In fact, the differences between them are often the most important aspects of the given religion.  The higher powers are different in their attributes, way to be worshipped, and interaction with mankind. Many of the morals are different.  The way of salvation/going to heaven is different.  These are the important details that have "life or death" consequences.

All faith systems could be false, but they cannot all be true.

The second line of evidence is the emerging field within sociology that gives strong indication that children have a natural tendency to believe God exists.  This affirms that the inherent default position is theism.  We don't have to know about these studies to recognize this.  People by default want to worship and believe in a higher power.  It's a universal human experience.  Though, some cultures have been known to influence children against this basic belief.  Of course, opponents of religion would take the opposite position.  Since this is an emerging field, there's not decades of research on the topic.  Those who are curious for more information can check of the sources quoted in the link above.

The third line of evidence is that it is perfectly reasonable to look at creation and think that everything was designed.  In fact, it's intuitive.

The atheist or agnostic who states that there is no evidence for the existence of God is excluding the material world by mere question begging.  They are assuming the thing they are trying to prove. While one interpretation of how the world came to be is completely materialistic, there are others that involve a creator.  An honest and open person would say that it is perfectly reasonable to look at the world and say that there is a Creator who made this.  In fact, even atheist Richard Dawkins has said as much:

         Yet the living results of natural selection overwhelmingly impress us with the appearance of design as if by a master watchmaker, impress us with the illusion of design and planning. (Cover)
        Biology is the study of complex things that appear to have been designed for a purpose. (1)

        Richard Dawkins, "The Blind Watchmaker"

The world looks designed.  Could this be because it is designed?  This isn't why early scientists of the middle ages thought that because God is orderly, His creation ought to be orderly?  This is the idea that helped spark modern science, and it was based in Christianity/theism.

As a quick aside, for those who are open minded and want to further investigate this, I encourage you to follow the "Anthony Flew example."  Anthony Flew was a prominent philosopher and atheist for a career of over 60 years.   In the late 1990's he began to seriously consider the evidences proposed by Intelligent Design proponents. In response to his studies, he left atheism for theism.  Intelligent Design had a been popularized in the early 1980's and continues to gain scientific credibility and peer reviewed papers.  The Discovery Institute is a think tank for intelligent design proponents in which you can learn much about their theory and findings.

The Anthony Flew Example is a challenge for agnostics and atheists to retrace Flew's steps and see the available evidence for an Intelligent Designer.  I encourage skeptics to use ID proponent's writings to evaluate the claims of ID instead of reading the rebuttal papers, which often straw man or don't understand the ID arguments. (If you want to read both, that's fine with me, just make sure the rebuttal paper is actually addressing and refuting the specific points made by ID proponents.) I think anyone who takes this challenge seriously will see that there are good reasons to believe that God exists.  Therefore, theism is more reasonable than agnosticism or atheism.

I would also like to note that the two main objections I've heard to this point is: 1) based on appeals to authority to reject ID instead of looking at the evidence for ID on its own merit, and 2) an appeal to future evidence.  This second appeal is based on the idea that ID is a type of "god of the gaps" argument.  First, it is not.  There are plenty of articles online explaining why, so I'll defer you to Google.  Second, we can only evaluate the evidence that exists so far.  Appealing to future evidence is begging the question (assuming that the evidence that will be uncovered one day will overturn ID evidences).  Let's deal with the evidence that we have now.  That's a very reasonable request.  When new evidence is announced, we can evaluate it in light of all the evidence that precedes it.  That's how science works.

Curiously, it seems those who reject ID have already been persuaded by evolution.  In that case, can one really say they are neutral?  They have already been influenced by an outside authority.  The idea of a default position is one that is gained by intuition and general life experience.  Whether science or religion is taught at a young age, then a question must be raised on what the difference between the real default position and a position one has been persuaded to.

Based on these three lines of evidence, I propose that the real default position is the theistic position. (Theism is simply the belief that God exists and deism is the belief that God exists but may not be involved in the world today.)  This is based on recognizing that not all faith systems can be true, but one can be; children naturally believe in a higher power, so that affirms theism as a default position; and the world appears designed, therefore intuition tells us it is.

So this is my argument for theism as the default position based on intuition, which is what a default position would entail.  There are other arguments from intuition that have been offered by others, most notably by CS Lewis, who advanced the Moral Argument and the Justice Argument.  The moral argument answers: Why do we have a sense of morality, or right and wrong?  Why do we seem to know that there are objective moral truths, like it's wrong to torture human babies for fun?  It seems intuitive that morality is built into our design for the human experience.  Anyone can deduce that since we sense a moral law, there must be a moral law giver.  The Justice Argument is one that answers the question why we have a notion of justice.  Why do we dislike injustice?  These can both be used to point to God as the source of these.

I've also offered additional reasons why theism is plausible based on Anthony Flew.  It takes the default position (which he didn't actually take originally) and takes it further.  It takes the reasonable notion of perceived design and tests it.  Based on that, Flew went from atheist to theist.

This conclusion is also compatible and affirmed by the Bible. Romans 1 states that the natural man knows that God exists:

        18 For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who suppress the truth in unrighteousness, 19 because what may be known of God is manifest in them, for God has shown it to them. 20 For since the creation of the world His invisible attributes are clearly seen, being understood by the things that are made, even His eternal power and Godhead, so that they are without excuse, 21 because, although they knew God, they did not glorify Him as God, nor were thankful, but became futile in their thoughts, and their foolish hearts were darkened.

        Romans 1:18-21

As a quick overview, we can see in verse 18-19 that mankind has a conscious that tells them when they break God's moral law. (Later in the chapter it states that people can sear their conscience so they no longer feel guilt or conviction.) Therefore, our conscious testifies to us that God exists, AKA the moral argument.

Then in verses 20-21 tell us that by the creation itself we can know/infer that God exists.

I recognize that some people will take issue with me saying that these intuitions make a default position.  While I do think this is a strong case, I'm willing to concede for the sake of the argument that agnosticism may be more accurately called the default position because it precedes intuition.  However, under this scenario, the default position is based in ignorance.  Theism is then one step from the default by adding intuition based on general human experience. 

So, hypothetically, even if theism is not the default position, I think it would still be considered the "starting position" for people who want to evaluate faith systems. I can't see why theism is not their starting position unless they have already been influenced by other sources.

This is my main reason why for saying that I think that not only is theism the most reasonable default position, but atheism is the most unreasonable position.