I contend that there is no scientic proof for the non-existance of ID, therefore it becomes an "act of faith" to declare the non-existance of ID.
There is no such thing as evidence of non-existence. Evidence doesn't work that way. There can only be evidence for positive assertions. The quick way of phrasing this, which you may have heard before, is "You can't prove a negative".
A positive assertion would be "Life is Intelligently Designed by some unknown agent." Now it would be the duty of the person making that assertion to give evidence for it if he wanted it to be accepted as fact. Every ID "theorist" has failed to present such evidence. So, it is not an act of faith to not believe in it. There is simply no reason to do so.
Conversely, by your own definition, it does in fact take an act of faith to believe it.
I stand by the statement that science only tells us how, it does not tell us why.
You are correct in this. The great metaphysical "why?" is simply not the concern of science. Science is not designed for answering such questions and is incapable of doing so. It is designed to find explanations for how the natural world works, which it excels at.