Vayeira. Sedom and Pilegesh b'Giv'ah

It is clear that when Shmuel Hanavi wrote Sefer Shoftim he described the events of Pilegesh b'Givah to correspond point by point to the behavior of the people of Sedom. After Binyamin was defeated, the other Shvatim prohibited intermarriage with the remaining women, just as an issur chitun was decreed on Amon and Moav.

The Ramban, for example, points out the correspondence, and finds a degree of distinction -

ודע והבן כי ענין פלגש בגבעה אף על פי שהוא נדמה לענין הזה (של סדום) איננו כמוהו לרוע, כי הרשעים ההם לא היה דעתם לכלות הרגל ממקומם, אבל היו שטופי זמה ורצונם במשכב האיש האורח, וכאשר הוציאו אליהם פילגשו נתפייסו בה

and

ובפרץ ההוא עוד לא היו בו כל אנשי העיר כאשר בסדום, שנאמר בו מנער ועד זקן כל העם מקצה, אבל בגבעה נאמר והנה אנשי העיר אנשי בני בליעל, מקצתם שהיו שרים ותקיפים בעיר כמו שאמר האיש ויקומו עלי בעלי הגבעה, ועל כן לא מיחו האחרים בידם

Similarly, the Malbim -

אנשי בליעל - ההבדל מחטא סדום הוא, בסדום חוקקו חוקים נשחתים מצד השכל וכאן עשו מתאותם הרעה, ולא רצו להרע לזקן שהכניסו לביתו לכן יצא אליהן בלי פחד, וכתיב "מתדפקים" עושים עצמם כדופקים ולא כבסדום שנגשו לשבר הדלת

The search for distinctions underlines the similarity.  It is hard to understand how a people described as inherently and essentially רחמנים, ביישנים, וגומלי חסדים could deteriorate to this level. Even if this event was limited to one small group, this did not take place in a vacuum.  Giva was a large and well populated area, and when Binyamin was confronted, they refused to punish the evil doers.

Binyamin was not like the other Shvatim. Chazal say that Eisav will only fall in the hands of the children of Rachel, Yosef and Binyamin. The Gemara says in many places that Binyamin was so desperate to be the host of the Shechina that the place of the main kedusha of the Mikdash is davka in his territory, Shiloh, Bayis Rishon, and Bayis Sheini.

I understand that people and groups change. Shimon and Levi were fustigated by Yaakov Avinu for their impulsive violence, and while we don't find that Shimon ever changed, Levi did come to embody the highest expression of Torah and Kedusha.  But the degree and nature of this change in Binyamin, the fall from the highest spirituality to utter debasement, from the cynosure of Klal Yisrael to its worst, מאיגרא רמה לבירא עמיקתא, is incomprehensible to me.  Imagine that Klal Yisrael would become Amaleikim and the Amaleikim would become like Klal Yisrael. This is beyond היהפך כושי עורו ונמר חברברתיו.

The following approach is the only one that makes any sense to me.  It is based on Rav Bergman in his new Shaarei Ora, with a few changes in emphasis.

The owner of the Pilegesh was from Har Ephraim.
The avoda zara of Micha, Pesel Micha, was located in Har Ephraim.
San 103b-

תניא רבי נתן אומר מגרב לשילה ג' מילין והיה עשן המערכה ועשן פסל מיכה מתערבין זה בזה בקשו מלאכי השרת לדוחפו אמר להן הקב"ה הניחו לו שפתו מצויה לעוברי דרכים ועל דבר זה נענשו אנשי פלגש בגבעה אמר להן הקב"ה בכבודי לא מחיתם על כבודו של בשר ודם מחיתם

Then, regarding Amon and Moav,

א"ר יוחנן משום רבי יוסי בן קסמא גדולה לגימה שהרחיקה שתי משפחות מישראל שנאמר (דברים כג, ה) על דבר אשר לא קדמו אתכם בלחם ובמים

The Maharsha there says that according to Rashi " בקשו מלאכי השרת לדוחפו means to push away Micha. But he explains it refers to the smoke from his maaracha. He explains that the two mixing columns of smoke were seen by everyone. People wondered how Hashem could allow this blasphemy to continue. They all decided that it was because of Micha's philanthropy. This is why the people didn't protest or interfere with Micha - because they said that it appears that Hashem tolerates his Avoda Zara because of his charity, so we too will leave him be.

Maharsha -

לדוחפו כו׳

 פרש"י למיכה ועוד נל"פ לדוחפו לעשן הפסל שהעשן של מערכה מתמר ועולה כמו ששנינו לא נצחה הרוח את עמוד העשן אבל עשן הפסל היה מתעקם ג' מילין והיה מתערב בעשן מערכה ובקשו מה"ש לדחוף אוחזתו עשן הפסל מעשן המערכה שלא יתערב בו

ועד"ז נענשו כו׳ ר״ל שזה הדבר שהיה פתו מצויה לעוברי דרכים הטעה את אנשי ישראל במעשה פלגש בגבעה שלא מיחו במיכה ובאו לעונש כזה שנפלו מהם מ׳ אלף שא״ל הקב״ה בכבודי כו׳

The Maharsha is saying that the בכבודי לא מחיתם was the reason hat in the first two battles between Binyamin and the others, Binyamin was victorious and forty thousand from the other Shvatim died in battle at the hand of Binyamin.

R Bergman asks, why was Binyamin not guilty of the same sin? They, too, ignored the avoda zara of Micha.  True, Klal Yisrael showed greater concern about what happened to the woman than about the biyayon of avoda zara, while Binyamin was indifferent to both. But does that make Binyamin the proper instrument to punish Klal Yisrael? They were almost equally guilty in ignoring Pesel Micha.
Certainly, their punishment was triggered by their horror and demand for justice for the crime against the Pilegesh. But the main sin of Klal Yisrael was that they ignored Pesel Micha. There had to be some reason that Binyamin was the right instrument for punishing the rest of Klal Yisrael. It has to be that whatever Klal Yisrael's sin was, Shevet Binyamin was completely clean of that sin.

She'eilas chacham chatzi teshuva. We began by describing the lofty spirituality of Shevet Binyamin, their consuming desire that the Shechina be in their cheilek.Yosef and Binyamin cried about their vision of the churban of Shilo and the Mikdash, as we saw in Breishis 45:14. Binyamin was so in obsessed with his desire for the Shechina that a strip of land came from his portion and entered into Yehuda's, upon which the mizbei'ach was built, and the Kodesh Kodoshim as well. It was this spirituality that led to their utter debasement.

Klal Yisrael tolerated Micha because they were saw that he lived undisturbed, and the smoke from his korbanos mixed with that of Shiloh. They realized, as Chazal did, that Micha's tranquility was due to his human kindness, his limitless philanthropy. They decided that all that matters in this world is bein adam l'chaveiro, Hillel's "Love thy neighbor as yourself." The mitzvos bein adam lamakom are less important, marginal. A man that dedicates himself to caring for his fellows is a great and good man, even if he brazenly and unashamedly transgresses on even the most fundamental of laws between man and God.

Shevet Binyamin knew that this was dangerously false. They knew that if a person, Jew or Gentile, casts away his obligations to his creator, he is not redeemed by his love for his fellow man. For Binyamin, the Shevet that was inebriated with their love for the Ribono shel Olam, Bein adam lamakom is the essence, and nothing else matters if that is missing.

Extremely disturbed by Klal Yisrael's false and dangerous error, Binyamin decided that they need to go in the opposite direction, to firmly state that bein adam lamakom is the most important thing. To this end, they intentionally de-emphasized the concept of bein adam l'chaveiro. Once you start on the path of not focusing on bein adam lechaveiro, you then begin to ignore it, and indifference turns to disdain.

This is why Amon and Moav are set apart - because they didn't bring us food and water, and they tried to kill us. That seems like a non-sequitor, or at least an incongruity. But it's not. Trajectories are set by little movements, and then acquire an inexorability.

This is a historical reality. As Rav Bergman says, bible proficiency became an inappropriate goal for the Orthodox because of the Christians, and dikduk because of the Maskilim. As Rabbi Nachman Bulman put it, We Orthodox can't have decorum in shul because of the Reform; we can't love Eretz Yisrael because of the anti-religious Zionists; and we can't hope for Mashiach because of the Lubavitchers. Soon there will be nothing left for Frum Jews. Rav Bergman just added studying Tanach and Dikduk.  But the fact remains that this does happen.

From this, Binyamin fell to a point where they were not horrified by the behavior that occurred in Givah, and their antipathy for the rest of Klal Yisrael meant they refused to listen to the demand for justice. In the first two battles, Binaymin was victorious, because they, at least, were initially motivated by their hatred for Avoda Zara. Ultimately, of course, they were vanquished, because the sin was in fact something that recalled the horrible behavior of Sedom.