If i am getting you. What you are saying is that:
1) Every "why" question need a purpose.
2) If A s existence IFF depend B s existence, then the unknowability of B implies the unknowability of A.
*) i don t understand what you mean by "the truth of christianity"? What is that mean? In fact, i dont really know what you mean by "a conception" for something to be ture. I have a conception of the dinner i ate? can you tell me the frame of mind i need to have a "conception" that something is "ture"?
1) Not every why need a purpose. Some might be just an emotional impulse. I don t see why we should stop asking. In fact, it is a bit sad you think this way. You are thinking yourself into a box.
2) I don t really see your point. I think it sort of prove my point.
If so, then you are really limited yourself. It makes no sense to me. Science can only provide genealizations of natural phenonmen, and summerized into a couple of "laws of nature". Perhaps one day, scienctists might come up with one or two equations that sort of describe everything important in our universe. What brings those equations to life? Why the hell would there be a universe for the equations to describe? Why our universe? I don t understand you at all. Your rational is : People should stop asking this question, because it has no answer.
We can ask "why" if and only if( the truth it require) science fail to provide a reason.
Science fail to provide reason for 1) existence 2) the laws of nature, 3) cannot explain why the laws have the form that they do. Therefore, the question of "why" can be asked.