I am not a Biblical Literalist, insinuate that those who claim to be
Biblical Literalists are hypocrites, and otherwise rant.
Luckily, I read and listened to worthwhile commentary, so the world is  
spared.
I do, however, have a question about how the sacrificial system  
worked, or if it even worked at all.  It seems very unsustainable, and  
these parshiot point out why.
In Metzora, we learn that women become tainted (unclean, ritually  
impure, etc) every time they have their periods, and they are tainted  
for a week following and until they bring a sacrifice and can not  
touch consecrated objects. This sacrifice is two birds, either pigeons  
or doves; one is a purification/sin offering, and the other is a burnt  
offering. So that's two sacrifices every four weeks, if you're a  
healthy woman who's not pregnant.
In Tazria, we learn that a woman is also tainted after childbirth, and  
remains so until she brings a sacrifice. If the baby is male, she is  
tainted for a week, just like when she has her period. If the child is  
female, it's two weeks. As if that wasn't enough, she stays tainted  
for another 33 days (boy) or 66 days (girl), until she brings a  
sacrifice. This sacrifice is a yearling lamb to be burnt and a pigeon  
or dove for purification/sin.
That's a lot, considering there would also be a thanksgiving offering  
for the child, which would probably be another lamb. But thinking in  
terms of sheer volume, I don't know that the system could work. There  
is only one Temple, only one altar, and only one set of priests. Each  
sacrifice must be performed in a specific place and according to exact  
instructions, or the priest risks getting frizzled. Each sacrifice,  
other than the burnt ones, must also be eaten completely and can only  
be eaten by the priests and their families.
Considering women who live in close proximity tend to "sync up",  
that's a lot of squab all at once. During these busy times and  
festivals, logic also breaks down, because the priests can only  
perform the ritual so quickly. I don't know if it was even possible to  
make more than two or three burnt sacrifices in any given day. Did  
people have to wait? What happened when they were time-sensitive?
My rabbi also doesn't know. I hope someday to understand.
The commentaries that stood out to me this week were from some usual  
suspects: the Pardes podcast, G-dcast, and one from Jewschool.com. It  
is from the jewschool article that I took the word "tainted" to use  
for <i>tumah</i>. Most translators use something with a negative  
connotation like "impure" (which implies sin), or "unclean" (which  
implies filth). Other, more liberal translators use the more neutral,  
but somewhat unwieldy "ritually impure". To me, tainted seems like a  
reasonable word to use. It describes an impure state, which fits the  
bill, but it also doesn't imply intention, unworthiness, or disease.  
It's just a state that requires a little action to correct, like  
refining, distillation, or sacrifice.
The Jewschool commentary also put a spin on the situation that made  
sense to me. To the commentator, being tainted with whatever tzara'at  
is wasn't necessarily a bad thing. You got some required time away  
from the public. It was time to think, time to reflect, time to grow  
as a person. And when your condition changed and improved, the  
sacrifice marked the transition in your life from tainted to pure  
(which are essentially synonyms for HaShem's favorite things to  
separate, the sacred and the profane/secular). The commentator also  
wrote a very beautiful reason for the ritual: "old opportunities are  
sacrificed to make way for new ones", reinforcing the idea that tumah  
is a lifecycle event. I can buy that.
The G-dcast for Metzorah talks more about the skin ailment parts than  
the lady-specific parts. He points out that modern doctors are unsure  
of what tzara'at describes. It doesn't seem to be any known disease,  
which somewhat paves the way for a supernatural explanation. I know  
that acne or herpes wouldn't be cured by this ritual (although the  
text isn't describing a cure). But since it can happen to homes and  
clothing as well as skin, it's not something easily explainable. It  
would have to be some kind of mold or fungus that occurs very  
selectively in the homes and on the clothes, and might cause the skin  
problems also, but the text implies that each can happen  
indepentently, and that it can happen to only one family member's skin.
This commentator says, as is traditional, that it was the result of  
<i>lashon hara</i> (evil tongue/gossip). This is clearly a  
supernatural explanation. However, it seems to fit, at least until you  
consider that tzara'at doesn't occur any more, even though gossip is  
prevalent. Even so, the effects of the tzara'at haven't necessarily  
disappeared. Evil tongue used to take away your home, your  
possessions, and your position in society. This is still possible  
today, and it does happen. The lesson we can learn here is that once  
the damage of gossip is done, it's very difficult to fix.
The Pardes podcast was also full of insight that I wouldn't have  
expected from these parshiot. He talks mostly about the category of  
"impurity that goes out from one's body", and how that logically also  
applied to childbirth. He says that the 40 (or 80) days in which a  
woman couldn't go to the Temple after childbirth or bring sacrifice  
are because if the close proximity of childbirth and death. (a note, I  
found this troubling, because a woman couldn't then attend her own  
son's brit milah).
The explanation goes that a dead body is the ultimate expression of  
impurity, and all impurity is associated with death. During  
childbirth, there is a great deal of blood. Large amounts of blood and  
death are often in the same place. There was also a high mortality  
rate associated with childbirth; both the mothers and the babies were  
at risk. So it might seem reasonable to think that there's at least a  
small amount of death in birth.
This commentator also points out that it wasn't always this way:  
sadness in childbirth was part of HaShem's curse to women in Eden. He  
also says, like the Jewschool commentary, a new mother might need some  
time away to get used to the new period in her life. He used the  
phrase "part of a woman has left her", and suggests that like today's  
mothers, women then also suffered post partum depression and the tumah  
time allowed them a chance to reflect on the transition.
The commentator goes a step further with the Eden comparison in order  
to tie tzara'at in to the parsha. Like the G-dcast commentator, he  
says that the cause was lashon hara. But he says that the snake in the  
Garden was the originator of the evil tongue, and is the reason that  
people who speak it become like living dead, and that the sacrifices  
allow people to affirm life and mark their commitment to becoming  
better people.