Why was the First Temple destroyed? Because of (the) three (cardinal) sins: idolatry, adultery and bloodshed ... But the Second Temple, when they engaged in Torah and mitzvot and good deeds, why was it destroyed? Because there was unfounded hatred (sin’at ḥinam). This teaches that unfounded hatred is the equivalent of violating the three cardinal sins. (Babylonian Talmud, Yoma 9b)
Firstly, we quote the stronger comment of Pitron Torah (late 9th – early 10th century Midrashic compilation): “unfounded hatred is the equivalent of all sins and offenses.”
Secondly, the Talmudic comment equating sin’at ḥinam and the three cardinal sins is a great understatement: the destruction of the First Temple, which resulted from violating the three cardinal sins, lasted only seventy years, while the second destruction, which was the consequence of sin’at ḥinam has lasted more than 1950 years!
It is necessary to understand the definition of “sin’at ḥinam.” Clearly, during the generation of the second destruction, there were significant differences of opinion among various groups of Jews: the nationalists who believed it was imperative to rebel against the Roman occupiers of the Land, the moderates, who sought an accommodation with the Roman authorities, those who were willing to submit to Rome’s rule, etc. No doubt, the differences of political opinion were the source of hatred among the Jews, so the hatred, seemingly, is not unfounded. I believe that the Sages teach us that, ultimately, any hatred among Jews is unfounded. It is legitimate to have differences of opinion, but it is unacceptable to allow these differences to generate hatred within the nation.
Indeed, this approach is clearly implied by Pitron Torah (Parashat Tzav), which states that Joseph’s brothers were guilty of sin’at ḥinam. Though the Torah explicitly states the reasons for the brothers’ hatred:
And his brothers saw that their father loved him more than all his brothers, so they hated him, and they could not speak with him peacefully. [Genesis 37:8]
And they hated him yet the more for his dreams and for his words. (See Rashi, who understands “his words” to refer to Joseph’s reports of the brothers’ negative behaviors) [ibid. verse 8]
nonetheless, this Midrash refers to their hatred as “unfounded.”
The great Torah commentator ibn Ezra (c. 1089 – 1164) understands a prohibition against “sin’at ḥinam” to be the inherent meaning of the negative mitzva: “You shall not hate your brother in your heart.” [Leviticus 19:17] Rabbi Shimon ben Ẓemach Duran (1361 – 1444) adds that this is mandated also by the positive mitzva: “you shall love your neighbor as yourself.” [Leviticus 19:18]
Perhaps it is more exact to say that Rabbi Duran’s comment parallels Rabbi Kook’s insight that it is through “ahavat ḥinam” (unbounded love) that “sin’at ḥinam” will be rectified. (David Magence)

Shabbat Shalom and a meaningful fast!
The Va’ad