We are now in the midst of the "three weeks" preceding Tisha Be'av, when we mourn the destruction of the ancient Temple in Jerusalem. The sages of the Talmud state that the Temple was destroyed due to sinat hinam - baseless, or gratuitous, hatred within the Jewish people.
The expression is a bit anomalous, especially for a social scientist trained to assume that people have reasons for everything. I would like to present one explanation for both the term and the phenomenon, drawing on the resources of ethics and social science.
One obvious benefit of hate is to induce us to protect ourselves from harmful individuals, people who it would be dangerous to be near. This could be because they are actually trying to harm us (such as a mugger or a terrorist), or because they are liable to influence our behavior in a way we identify as harmful (such as a dope peddler).
There is nothing baseless or gratuitous about hatred like this. But there are still isolated individuals who manage to rise above even this very practical kind of hatred - people such as Bruria, who taught we should hate only the sin, not the sinner.
However, another benefit of hate is to improve the cohesiveness of some social group. It is a short step from noticing that adversity increases solidarity to realizing that inciting adversity may be a useful tool for bolstering solidarity within some group.
Such "instrumental" hatred is not gratuitous in the sense of being without benefit or reason, but it is gratuitous in the sense that the object of hatred isn't being hated because of any particular iniquity. Rather, the chosen enemy just happens to be in the wrong place at the wrong time - a time and a place where hating somebody happens to be useful.
(Rashi's definition of baseless hatred: "He didn't find any sin in him for which it would be permissible to hate him, and [even so] he hates him.")
Of course, hating people has costs as well: there are immense benefits to cooperation and friendship, which tend to be destroyed by outbursts of hatred. For this reason, we would expect that instrumental hatred would be particularly cultivated when its object is powerless to retaliate.
One instance would be a powerless alien group, such as the Jews in exile. Jews often wonder what it is about them that arouses the scourge of anti-Semitism almost everywhere they wander. But it need not be anything in particular that Jews do; sometimes it is just useful to hate someone, and the Jews are a convenient someone. It's nothing personal.
(Remember the kindly Constable in Fiddler on the Roof? "Just some mischief, so if an inspector comes through, he can see we did our duty. I don't know why there has to be this trouble between people. But I thought I should tell you.")
Almost the opposite can take place in a free society. Fortunately, in a free society, innocent identity groups cannot be oppressed merely because they are different. But it can also be difficult to prevent a group from cementing its own solidarity by relating to its host society as a whole, or to some competing subgroup, as "the great Satan" or the like. There may be no particular trait arousing enmity and suspicion; it's just a matter of convenience and nothing personal. In other words, it is sinat hinam.
I believe such "instrumental hatred" between factions was responsible 2,000 years ago for corroding the Jewish polity and the last remnants of Jewish sovereignty, those collective institutions that enabled the Temple to survive. I also believe both kinds of instrumental hatred - that from without, if we are too powerless, and that from within, if we are too divided - have the potential to threaten our collective survival again.
Most of all, I am convinced that if we are wise enough to heed the message of our sages, and recognize the unique nature and the unique threat of this special, seemingly gratuitous type of enmity, we can keep it to a minimum and continue to thrive as a united society.
Asher Meir is research director at the Business Ethics Center of Jerusalem, an independent institute in the Jerusalem College of Technology (Machon Lev).