לא משהינן אלא כייפינן ליה מיד כיון דאמרה מאיס עלי שהרי אין בנות ישראל הפקר כל כך שיהו משועבדות ליבעל למי שמאיס להםRamban on Exodus 22:15 also has this language, in his discussion of how the Torah seems to force a woman to marry her rapist. He thinks it is pshat in the Torah that its her decision, not the rapists, and he provides this interesting reasoning:
ועל דעת רבותינו (כתובות לט ב): גם שם בין היא בין אביה יכולין לעכב כי איננו הגון שיקחנה על כרחם, ויעשה עמה שתי רעות, ופעמים שתהיה נכבדת ממנו ולא יתכן שתתבזה בחטאו, והמשפט הישר שיהיו הנישואין בידה ולא בידו, שהוא ישאנה על כורחו שלא יהיו בנות ישראל הפקר לבעלי הזרוע.
This accords with our rabbis, "Either she or her father can refuse," for it is not proper for her to be married against her will, which would be two evils for her [both rape and forced marriage], and sometimes she is in a higher social class than him and his sin would not cause her social embarrassment [such that she would be bereft of other marriage options]. And the moral law is that marriage is her right, not his, that he would be married to her against his will. For the daughters of Israel are not hefker for brutish men.Rambam also uses this phrase. In his context, if women are treated as hefker, it will lead to promiscuity. Its in Yesodei HaTorah 5:9:
מי שנתן עיניו באשה וחלה ונטה למות ואמרו הרופאים אין לו רפואה עד שתבעל לו ימות ואל תבעל לו אפילו היתה פנויה ואפילו לדבר עמה מאחורי הגדר אין מורין לו בכך וימות ולא יורו לדבר עמה מאחורי הגדר שלא יהו בנות ישראל הפקר ויבואו בדברים אלו לפרוץ בעריות.
Of course, the Mordechai's language above sounds somewhat similar to the Rambam's formulation of the law when a women claims her husband is disgusting to her. In Rambam's language (Mishneh Torah, Ishut 14:8), she is not a "captive" that she should be forced to be with someone she finds repulsive:[When] someone becomes attracted to a woman and is [love-]sick [to the extent that] he is in danger of dying, and the physicians say he has no remedy except engaging in sexual relations with her, he should die rather than engage in sexual relations with her, even if she is unmarried.He is even not to be given instructions to speak to her [in private] behind a fence. Rather, he should die rather than be given instructions to speak to her behind a fence, so that Jewish women would not be hefker, and these matters would lead to promiscuity.
אם אמרה מאסתיהו ואיני יכולה להבעל לו מדעתי כופין אותו לשעתו לגרשה לפי שאינה כשבויה שתבעל לשנוא לה
If she says, "Because I am repulsed by him and I cannot voluntarily engage in relations with him," her husband should be compelled to divorce her immediately. For she is not like a captive, that she must engage in relations with one she loathes.Let's note that the Rambam uses the opposite language to describe Jewish women. Whereas we have seen the phrase "hefker", meaning so loosely kept or wanton, Rambam in this context says she is not "captive", as in not free or able to move. I think that's interesting.
The Yad Ramah, Sanhedrin 21a, discusses why there is an institution of marriage with kiddushin and ketubah if concubinage works. He states its the rabbis making a decree because of this familiar aphorism:
אבל אם רצה לייחד אשה בלא כתובה ובלא קידושין מדאורייתא שפיר דמי ורבנן הוא דגזור כדי שלא יהיו בנות ישראל הפקר
If he wants to seclude himself with a woman without a ketubah and without kiddushin, on a Torah level it is fine, and it is the rabbis who decreed [these two things] so that the daughters of Israel would not be hefker.Let us look at a comment of Rashi on Genesis 34:31. Jacob is upset that Simeon and Levi have wiped out the entire city of Shechem. Their response is. "Shall he make our sister like a harlot?" Meaning, they had to fight for their sister because leaving her in such dire circumsatnces would be to say she is like a zonah, a harlot, that they are not concerned with her welfare, especially her sexual welfare. Rashi has a one-word comment on "zonah", which is not harlotry to him. He says it means, based on Genesis Rabbah 80:12, the word word we love so much, "הפקר". Meaning, in the midrash and Rashi's reading, they were saying, "Our sister is not so hefker!"
Lastly, I'll point out this phrase precedes the rishonim. The Mishna in Yevamot 13:1 states:
אמרו להן בית הלל לבית שמאי: ממאנת והיא קטנה, אפלו ארבעה וחמשה פעמים. אמרו להן בית שמאי: אין בנות ישראל הפקר, אלא ממאנת וממתנת עד שתגדיל, ותמאן ותנשא.
Beit Hillel said to Beit Shammai: A girl may refuse [exercise refusal] as a minor even four or five times. Beit Shammai said to them: The daughters of Israel are not hefker, rather she may refuse and then wait to attain maturity, or refuse and be married.Jewish women have rights, declare the Mishna and Rishonim! Some use it in a way that means that we are afraid women will be abused sexually, but others use it to mean they have rights to freedom and choice as human beings!