Rav Y Henken replied to my previous entry on this subject (repeated here for the benefit of Google). He wrote:
See in my “New Interpretations on rhe Parsha” (Ktav) and also Shu”t Bnei Banim vol. 4 maamar 22.
Q. Why is a woman in childbirth considered to be ritually impure?
A. That is a difficult question. Vayikra is full of laws of tumah and taharah. One of the six orders of the Mishnah is devoted to them. But there is little discussion of the meaning behind ritual impurity, and why it should be forbidden in the Temple.
To be sure, tumah is often connected with death and decay, and as such can be seen as antithetical to the idea of haShem, the living G-d. This would explain why the most potent source of tumah is the human corpse, and why various types of animal carcass