from a documentary standpoint:
1. Authorship bias -
2. Survival bias -
3. Writing and application/interpretation isn't the same. "Catholic viewpoints" have changed over time but their application has changed even more, which is more important. You're arguing that there's a 1:1 correspondence.
from a "why bother studying the middle ages at all" standpoint
1. We can still talk women in the past without agreeing that they are vessels of weakness, sin and impurity and need to be treated with a firm hand
2. We can still talk homosexuals in the past without regarding them as sodomites who have fouled the clear spring of friendship, Augustine-like
I'm basically not sure what the problem is. We can full well disagree with the sources and their authors on any number of subjects, based on our vastly wider and deeper collective knowledge, so why not this subject. The call to examine the past from a strictly conservative viewpoint is hardly agenda-free.
Uhm, no, we can't really disagree with the sources. We can use different sources, and explain why they're better, or we can use the sources themselves and try to point out inconsistencies/issues, or we can use other sources of information (like archeology, etc.) But in the end we *must* rely on sources (and interpretation of sources) even recognizing that yes, sources are often incomplete, biased, etc.
History begins and ends with sources. We can't say anything outside of them (beyond "We don't really know about that.")