My point in using confessional (or any of the other descriptors I have tried out on this blog) is that scholars who are so invested theologically in a religious tradition and its maintenance are willing to suspend what we know to be factual about our world in order to read their scriptures as fact. These scholars confuse their confessional tradition with history and justify it as history, when in fact what they are justifying is actually theology.
Can a Christian be a historian of Christianity? Of course. But I would qualify this: only if that Christian is not invested in maintaining Christian theology as history in their academic contributions. That Christian must first and foremost be operating critical of the religion, and must be unwilling to cave in to the pressure of making theological claims historical knowledge. So training in historical-critical method is essential, as is vigilance in maintaining this orientation.