A few years ago, NT scholar Andrew Lincoln published a book attacking the Virgin Birth. Jason did a multipart critical review:
And I did some posting:
Now, however, I'd like to draw attention to something else. Does Lincoln have an ulterior motive for undermining the historicity of the Virgin Birth? Last year he contributed to a book in which he makes some revealing statements about his theological motivations:
My views about the truth of the Bible and its relation to faith continue to evolve in response to…factors, such as…church life and its mission of social justice, friendships. Times of radical questioning have been precipitated not by academic study of the Bible but more by crises in my personal life and relationships, by my and the church's failure to be loving…
So there was immediately a much greater recognition that the Bible's authority was not to be thought of as timeless in some unqualified sense. That deepening recognition was already preparing me to think about questions that confronted me in the first two setting in which I taught–about women's ordained ministry at Gordon-Conwell Theological Seminary and about homosexuality at St. John's College, Nottingham. Although I started off by thinking that traditionalists had the better exegetical case on these matters and that should be decisive, my pastoral experience with women students, who were highly gifted in teaching and preaching, and with gay ordinands, who had prayed and agonized about their sexuality for years and were placed in the invidious position of hoping their future bishops would be those who deliberately turned a blind eye to official teaching, caused me to rethink what the Bible's authority meant in such cases…This involves, as some put it, "improvising"… I (Still) Believe: Leading Bible Scholars Share Their Stories of Faith and Scholarship (Zondervan 2015), 148-149.
So Lincoln has a social agenda. He doesn't begin with principles, but people. He adapts and changes his view of Biblical authority based on personal experience and personal relationships.
Given his frank admission, you can see how attacking the historicity of the Virgin Birth (or the historicity of John's Gospel) drives another wedge into the authority of Scripture, thereby making room for his "social justice" concerns.