"It is said that if you know your enemies and know yourself, you will not be imperiled in a hundred battles; if you do not know your enemies but do know yourself, you will win one and lose one; if you do not know your enemies nor yourself, you will be imperiled in every single battle."
To know your enemy is the cardinal rule of warfare. When I served in the Marines while we were in infantry training school we were taught about common enemy weaponry and equipment. We were shown how to disable certain types of tanks and vehicles etc. Of course debating theists is not exactly considered to be war or anything that even remotely resembles combat. But the truth of the matter is that it can be approached in the same manner. What you have are two feuding ideologies and you must know and understand them both before you can engage in some sort of reasonable refutation.
"Take the helmet of salvation and the sword of the Spirit, which is the word of God." Ephesians 6:17
The word of God or the bible is referred to in the scriptures as the believers primary offensive weapon. If you know what is in that word and can demonstrate its flaws and inconsistencies competently then you will defeat superstition by turning its own weapon against them. Of course there are those who will deny anything you show them or resort to their insane rationalizations: you are taking that out of context; you don't understand the texts; you are interpreting it incorrectly, etc.
By understanding the fundamentals of Christian beliefs you can begin to rip that weed out by the roots! Some will cling tenaciously to those things that they cannot refute much less prove and they will fall back on their favorite defense of faith. Believe it or not I have come to the conclusion that one man who truly understood the power of religion over the masses was Adolf Hitler. I stand where he stood on the matter of faith. Here is a quote on this issue:
“It is always more difficult to fight against faith than against knowledge.”
Let's examine this a little closer. Why do you think that Hitler thought that is was more difficult to fight against faith than knowledge? Let's see what the bible defines as faith in the book of Hebrews 11:1 "Now faith is confidence in what we hope for and assurance about what we do not see." (NIV)
By this definition faith is a sort of hope in the unseen and an assurance or a certainty that what you believe is true. Faith does not rely on research, experimentation, or scientific inquiry. It is entirely independent of all other means of obtaining knowledge.
Faith is not only a mental but an emotional response to what you think you may know and it is as such driven by emotions and not knowledge. Hitler had something to say about that too in relation to emotions and reason:
“I use emotion for the many and reserve reason for the few”
Straight from the master of propaganda himself! Emotions don't respond to reason they never have and they never will. One of the things I learned as a former fundamentalist believer is that there were no words that could convince me that God was not true. The reason was because I was sure that I felt his presence around me at all times. I was certain that he spoke to me in my dreams and gave me visions. I believed that I felt his holy spirit coursing through my body when I prayed, preached, and ministered.
Experience trumps reason every time! There is no amount of reason that will convince this lady or any of the others laid out on the carpet that there is no God. Or that their experiences are not of God but are rather the result of elevated psycho-emotional states based on their indoctrination and presupposed beliefs. This is what you are up against when you try to refute theists! The more fundamentalist that they are the harder it is to get through to them. Some people will never be free from religion or irrational superstitions because they did not come to those beliefs rationally.
The best way in my opinion to handle some of these people is through demonstrating to them that you have a good command of the scriptures that they profess believe in. It's ironic that when you go back to the armor of God that the defensive weapon happens to be the shield of faith.
"In addition to all this, take up the shield of faith, with which you can extinguish all the flaming arrows of the evil one." Ephesians 6:16 (NIV).
Faith can see beyond the contradictions in the bible, faith assures you that what you feel is real and true, faith grounds you and makes you impervious to reason. One aspect of faith that many believers don't take into account and which is evident in their argumentation is that faith does not allow you to see or think clearly. In fact the N.T. admits this:
"For now we see only a reflection as in a mirror; then we shall see face to face. Now I know in part; then I shall know fully, even as I am fully known." 1 Corinthians 13:12 (NIV).
Granted the chapter referenced refers mostly to the virtues of love above all things. But within the context of describing love it makes reference to several of the gifts of the Spirit. It states that through most of those gifts we see things in part but ends with the promise that in the future all things will be revealed. The end of a believers faith is the completion of what he/she had hoped for their entire lives. You see how understanding the scriptures as they do helps you to come down to their level and interact with them?
Using to bible to discredit the bible is a very effective strategy and it is akin to speaking to a child on their own level of understanding. In the end though it is just a way to point them in the right direction. To help them ask the right questions and learn to use their reason unencumbered by faith. Leaving the fold is a very difficult decision to make and it is a journey that one has to make for themselves. We can point the way but we can't lead anyone to the right conclusions, that is left entirely up to them.