Carefully defining doubt is a need. Job has already been cited as an important example. Habakkuk challenges God when His ways seem to contradict His standards, and challenges the answer to his first question. “I believe; help my unbelief” seems to be cited positively. But there are also passages such as James 1:6-8 that are critical of doubting. The key aspect seems to be the attitude behind the doubt. Attitude is of course quite difficult to judge; even in person it may not be obvious, and the often brief sketches in Scripture often leave more to be inferred. Do not doubt what you have good cause to trust, but do not fear asking when you are uncertain, might get at the distinction. The “doubter” of James 1 seems to be one who is merely hoping to get something out of God, if He exists, rather than one who is seriously pursuing the question.