Jay Adams, the founder of nouthetic counseling, based his entire method on the premise that believers are more qualified to counsel, based solely upon their faith, than an unbeliever.
I found this gem of a quote today from John Calvin (Institutes 2; 2; 15).
Calvin would argue that Adams view is a despising of the gifts of the Spirit, and an insult to the Giver.
15. Therefore, in reading profane authors, the admirable light of truth displayed in them should remind us, that the human mind, however much fallen and perverted from its original integrity, is still adorned and invested with admirable gifts from its Creator. If we reflect that the Spirit of God is the only fountain of truth, we will be careful, as we would avoid offering insult to him, not to reject or condemn truth wherever it appears. In despising the gifts, we insult the Giver. How, then, can we deny that truth must have beamed on those ancient lawgivers who arranged civil order and discipline with so much equity? Shall we say that the philosophers, in their exquisite researches and skilful description of nature, were blind? Shall we deny the possession of intellect to those who drew up rules for discourse, and taught us to speak in accordance with reason? Shall we say that those who, by the cultivation of the medical art, expended their industry in our behalf were only raving? What shall we say of the mathematical sciences? Shall we deem them to be the dreams of madmen? Nay, we cannot read the writings of the ancients on these subjects without the highest admiration; an admiration which their excellence will not allow us to withhold. But shall we deem anything to be noble and praiseworthy, without tracing it to the hand of God? Far from us be such ingratitude; an ingratitude not chargeable even on heathen poets, who acknowledged that philosophy and laws, and all useful arts were the inventions of the gods. Therefore, since it is manifest that men whom the Scriptures term carnal, are so acute and clear-sighted in the investigation of inferior things, their example should teach us how many gifts the Lord has left in possession of human nature, notwithstanding of its having been despoiled of the true good.