i) In debates, Bart Ehrman appeals to critical consensus. Critical consensus is a subset of scholarly consensus. Critical scholarship is a euphemism for Bible scholars who don't believe the Bible.
It's amusing when people like Ehrman chide believers for failing to use critical scholarship as their yardstick. In effect that means believers should make unbelievers the standard of comparison. But why should believers adopt the viewpoint of unbelievers? That's nonsensical. Moreover, that assumes the very issue in dispute.
ii) In addition, there's a pecking order among Bible scholars. Some Bible scholars (liberal, moderate, conservative) are very talented. And they establish the paradigm within which other Bible scholars operate. You have a handful of ideological leaders; the rest are followers.
Many landed jobs as OT or NT professors, not due to any outstanding ability on their part, but because they knew the right people and went to the right schools. They have degrees from institutions that look good on a resume. They ingratiate themselves with big-name mentors who write glowing letters of reference. They dutifully regurgitate the current academic fads. In general, critical consensus doesn't represent an independent convergence of thoughtful scholars.
iii) Consensus isn't necessarily a bad thing. Sometimes it's a good thing. However, consensus breeds intellectual complacency. People stop asking questions once they think they know the answers. They just default to the received answers. Justification becomes circular: it must be true because so many people believe it, and so many people believe it because it must be true.
Most critical scholars don't think for themselves. They simply ride the wave of preexisting consensus within their insular academic shame culture.