It's not just women:
The Mishna sums up sources of Tumah:
(א) אֲבוֹת הַטֻּמְאוֹת, הַשֶּׁרֶץ, וְשִׁכְבַת זֶרַע, וּטְמֵא מֵת, וְהַמְּצֹרָע בִּימֵי סָפְרוֹ, וּמֵי חַטָּאת שֶׁאֵין בָּהֶם כְּדֵי הַזָּיָה,
(1) The fathers of impurity are a: sheretz, semen, [an Israelite] who has contracted corpse impurity, a metzora during the days of his counting, and the waters of purification whose quantity is less than the minimum needed for sprinkling.
(א) שְׁמוֹנָּה שְׁרָצִים הָאֲמוּרִין בַּתּוֹרָה. וְהֵן הַחלֶד וְהָעַכְבָּר וְהַצָּב וְהָאֲנָקָה וְהַלְּטָאָה וְהַכֹּחַ וְהַתִּנְשֶׁמֶת וְהַחֹמֶט. טֻמְאַת כֻּלָּן שָׁוָה וְהֵן הַנִּקְרָאִין שֶׁרֶץ לְעִנְיַן טֻמְאָה:
(1) The eight crawling animals that are mentioned in the Torah are: the weasel, the mouse, the ferret, the hedgehog, the chameleon, the lizard, the snail, and the mole. The impurity of them all is the same. They are each referred to as a sheretz with regard to impurity.
(ב) לְמַעְלָה מֵהֶם, נְבֵלָה, וּמֵי חַטָּאת שֶׁיֶּשׁ בָּהֶם כְּדֵי הַזָּיָה
(2) Above them are nevelah and waters of purification whose quantity is sufficient to be sprinkled
(ג) לְמַעְלָה מֵהֶן, בּוֹעֵל נִדָּה... לְמַעְלָה מֵהֶן, זוֹבוֹ שֶׁל זָב וְרֻקּוֹ וְשִׁכְבַת זַרְעוֹ וּמֵימֵי רַגְלָיו, וְדַם הַנִּדָּה...
(3) Above them is one who had intercourse with a menstruant ... Above them is the issue of a zav, his spit, his semen and his urine, and the blood of a menstruant...
(ד) לְמַעְלָה מִן הַזָּב, זָבָה ... לְמַעְלָה מִן הַזָּבָה, מְצֹרָע...לְמַעְלָה מִן הַמְּצֹרָע, עֶצֶם כַּשְּׂעֹרָה... חָמוּר מִכֻּלָּם, הַמֵּת...
(4) Above the zav is the zavah ... Above the zavah is the metzora... Above the metzora is a [human] bone the size of a barley grain ... More strict than all these is a corpse ...
"Tum'ah is the result of our confrontation with the fact of our own mortality. It is the going down into darkness. Toharah is the result of our reaffirmation of our own immortality. It is the re-entry into light."
(Tum'ah and Toharah: Ends and Beginnings)
This appears to make sense in the cases of the corpse, the loss of potential life associated with either female or male genetical emissions, or leprosy. It is conceivable that Sheretz impurity started as an association with death, even if by medieval times the list of species no longer makes sense.
But the biggest problem is that there are things that we might thing should be Tamei that are not, and things that we might think are Tahor but are not. The two examples I bring are:
(ג) אֵלּוּ שֶׁאֵין חוֹצְצִין ... וְלִכְלוּכֵי צוֹאָה שֶׁעַל בְּשָׂרוֹ, וְצוֹאָה שֶׁתַּחַת הַצִּפֹּרֶן ...
(3) The following do not block [purification through immersion in a Mikveh]: ... moist excrement on the body, excrement inside the finger nail ...
(ו) ... כִּתְבֵי הַקֹּדֶשׁ מְטַמְּאִין אֶת הַיָּדַיִם, וְסִפְרֵי הוֹמֵרִיס אֵינוֹ מְטַמֵּא אֶת הַיָּדַיִם. ...
(6) ... Holy Scriptures defile the hands, but the books of Homer do not defile the hands. ...
"When Lisa Berman was Education Director at the mikveh Mayim Hayyim ... she gave me the gift of translating Tumah as 'everyday state' and taharah as 'elevated state' which I think makes a lot more sense."
Rabbi Danya Ruttenburg
I now want to turn specifically to Niddah. The editor of the volume on the Jewish Women's Archive in which Rachel Adler's article can be found expresses the feminist critique of Niddah succinctly:
"The laws of niddah raise several issues of concern to women - and particularly feminists ... Perhaps the most vexing is: Why were the restrictions imposed upon the menstruating woman retained after the destruction of the temple, while all other forms of tum'ah were allowed to lapse... Furthermore, is there really no stigma attached to the concept of tum'ah, especially as practiced in the isolation of the niddah? She is treated, after all, as though bearing a rather unpleasant contagious disease. The prolongation of her period of tum'ah for seven days after the cessation of her menstrual flow reinforces the impression that the menstrual blood itself has powerful contaminating properties which must be guarded against."
Powerful stuff.
"The law protects women from the importunities of their husbands at a time when they are not physically and emotionally ready for coitus."
W Gunther Plaut, the Torah, a Modern Commentary.
However, this argument 'butters no parsnips'. One of the most unpleasant Mishnayot is:
(א) תִּינוֹקֶת שֶׁלֹּא הִגִּיעַ זְמַנָּהּ לִרְאוֹת וְנִסֵּת, בֵּית שַׁמַּאי אוֹמְרִים, נוֹתְנִין לָהּ אַרְבָּעָה לֵילוֹת. וּבֵית הִלֵּל אוֹמְרִים, עַד שֶׁתִּחְיֶה הַמַּכָּה. הִגִּיעַ זְמַנָּהּ לִרְאוֹת וְנִסֵּת, בֵּית שַׁמַּאי אוֹמְרִים, נוֹתְנִין לָהּ לַיְלָה הָרִאשׁוֹן. וּבֵית הִלֵּל אוֹמְרִים, עַד מוֹצָאֵי שַׁבָּת, אַרְבָּעָה לֵילוֹת. ...
(1) In the case of a young girl whose time to see a menstrual flow, i.e., the age of puberty, has not yet arrived, and she married and engaged in intercourse and her hymen was torn, Beit Shammai say: The Sages give her four nights after intercourse during which the blood is attributed to the torn hymen and she remains ritually pure. Thereafter, any blood is assumed to be menstrual blood and renders her impure. And Beit Hillel say: The blood is attributed to the torn hymen until the wound heals. In the case of a young woman whose time to see a menstrual flow has arrived but she has not yet begun to menstruate, and she married and engaged in intercourse and her hymen was torn, Beit Shammai say: The Sages give her the first night during which the blood is attributed to the torn hymen. Thereafter, any blood is assumed to be menstrual blood. And Beit Hillel say: The blood is attributed to the torn hymen until the conclusion of Shabbat, and she may engage in intercourse with her husband for four nights, as it was customary for a virgin to marry on Wednesday. ...
We should, however, contextualize this: child brides were part of wider society in those days. So there is contemporaneous Roman law about the same topic:
Ulpian, in Justinian's Digest 48.5.14.8
"Si minor duodecim annis in domum deducta adulterium commiserit, mox apud eum aetatem excesserit coeperitque esse uxor, non poterit iure viri accusari ex eo adulterio, quod ante aetatem nupta commisit, sed vel quasi sponsa poterit accusari ex rescripto divi severi, quod supra relatum est."
This said, I wish to also point out that however strong and valid the feminist critique of Niddah is, Tumat Baal Keri is also used to oppress men and boys. This one I was taught at Yeshiva:
(א) אָסוּר לְהוֹצִיא זֶרַע לְבַטָלָה. וְעָוֹן זֶה חָמוּר מִכָּל עֲבֵרוֹת שֶׁבַּתּוֹרָה. וְאֵלּוּ שֶׁמְּנָאֲפִים בַּיָּד וּמוֹצִיאִים זֶרַע לְבַטָּלָה, לֹא דַי לָהֶם שֶׁאִסּוּר גָּדוֹל הוּא, אֶלָּא שֶהָעוֹשֶׂה זֹאת, הוּא בְנִדּוּי, וַעֲלֵיהֶם נֶאֱמַר, יְדֵיכֶם דָּמִים מָלֵאוּ, וּכְאִילּוּ הוֹרֵג אֶת הַנֶּפֶשׁ. וּרְאֵה מַה שֶּכָּתַב רַֹשִ"י בְּפָרָשַת וַיֵֹשֶב בְּעֵר וְאוֹנָן שֶׁמֵּתוּ בְּחֵטְא זֶה. וְלִפְעָמִים בְּעֹנֶשׁ זֶה, חַס וְשָׁלוֹם, בָּנָיו מֵתִים כְּשֶׁהֵם קְטַנִים, אוֹ שֶׁיִהְיוּ רְשָׁעִים, וְהוּא בָא לִידֵי עֲנִיוּת.
(1) It is forbidden to discharge semen in vain. This is a graver sin than any other in the Torah. Those who masturbate and thus discharge semen in vain, not only do they commit a grave sin, but also one who does this is placed under a ban. Concerning such people it is said, "Your hands are full of blood," and it is likened to killing a person. See what Rashi wrote in the Sidrah of Vayeishev concerning Er and Onan, who died because of committing this sin. Occasionally, as a punishment for this sin, God forbid, one's children die when young, or grow up to be wicked, while the sinner is reduced to poverty.
(ה) אָדָם מֵאָה וּתְלָתִין שְׁנִין שִׁמֵּשׁ בְּרוּחִין נוּקְבִין, עַד דְּאֲתַת נַעֲמָה וּמִגּוֹ שַׁפִּירוּ דִילָהּ טָעוּ בְּנִי הָאֱלֹהִים בַּתְרָהּ עַזָ"א וַעֲזָאֵ"ל וְאוֹלִידַת מִנַּיְיהוּ. וּמִנָּהּ אִתְפַּשְׁטוּ רוּחִין בִּישִׁין וְשֵׁדִין בְּעָלְמָא, דְּאִיהִי אָזְלַת וּמְשׁוֹטֶטֶת בְּלֵילְיָא (נ"א בלילית) וְאָזְלָת בְּעָלְמָא וְחָיְיכַת (נ"א וחייכן) בִּבְנִי נְשָׁא וְעַבְדֵי לוֹן דְּאוֹשְׁדוּן קֶרִי. וּבְכָל אֲתַר דְּאַשְׁכְּחָן בְּנִי נְשָׁא נַיְימִין יְחִידָאִין בְּבֵיתָא שָׁרָן עֲלַיְיהוּ וְאֲחִידָן לוֹן וּמִתְדַּבְּקָן בְּהוּ וְנָטְלֵי מִנַּיְיהוּ תֵּאוּבְתָּא וְאוֹלִידָן מִנַּיְיהוּ. וְתוּ (יא ע"א) פָּגְעִין בֵּיהּ בְּמַרְעִין וְלָא יָדַע. וְכָל דָּא בִּגְרִיעוּ דְסִיהֲרָא.
(5) Adam had intercourse with female spirits for 130 years until Na'amah came. Because of her beauty, she led the sons of Elohim, Aza and Azael astray. She bore them all sorts of new kinds of Kelipah. Evil spirits and demons spread out from her into the world. They wander around the world during the night, deriding human beings and causing nocturnal pollution. Wherever they find men sleeping alone in their own homes, they hover over them and cling to them, arousing lustful desires and having offspring by them.
"At a later date, the Chachamim abolished the Takana...Some Rishonim explain that it was abolished entirely ... Others maintain that it was abolished only in regard to learning, but for davening, the Takana is still in place. The accepted halacha is that Takanas Ezra has been completely abolished, and according to the letter of the law, one may learn and daven in a state of impurity.
"When the Rambam was confronted with the question on why he had ruled leniently in regard to Takanas Ezra (for he only classifies it as a custom, not a requirement), he replied8 that although he personally never missed a tevila, even once, he could only write that which was halachah.
How do we understand Tumah?
Impure?
Associated with death?
Everyday?
Not a state to perform sacrifices?
Most Tumah is no longer used in Orthodox Judaism apart from
- Niddah (open to feminist critique)
- Tum'at Keri (could we call this open to feminist critique too)?
Is there any possible meaningful reconstruction of the laws of Tum'ah and Taharah?