Argument from incredulity, God of the Gaps, subtype of argument from ignorance
The argument, "I don't believe that ..." is particularly common amongst creationists and proponents of intelligent [sick] design theory.
This is a form of argument from ignorance in which the incredulous debater refuses to believe in a particular line of evidence (denial), or an interpretation of evidence that supports an alternate conclusion to that which the debater favors. The argument from incredulity essentially takes the position that personal reluctance to believe that something is true (or false) is a good reason for unfounded insistence that it is not true (or false). The fallacy lies in the segue from opinion to attempts at justification. The fact remains that while incredulity may be justified in that disbelief may have good grounds, it also may not be justified. The problem is simply that incredulity alone is not sufficient argument for or against a fact or interpretation.
In the history of human attempts to understand their universe, supernatural explanations–Gods of the Gaps–provided a framework for explanation in the absence of scientific comprehension. Humans invented deities to fill gaps in their understanding. Modern science offers the opportunity for comprehension, but many with an emotional need to believe literally in dogma are patently not interested in attaining true understanding.