I too like Sedaka's maxim: “Don’t hate your enemy”.
(As with so many other words, the definition of "hatred" is constantly being widening and weakening from "deep and emotional extreme dislike" to mere criticism of legally "protected" groups who can then financially and professionally damage such speakers - supported by a growing popularity for repression, but that is a discussion for another day.)
Using hatred in it's "true" historical sense, I read an interesting discussion of the history of hatred within the IDF which quotes the head of the Palmach, Yigael Allon in 1962: “There is no need to hate the enemy in order to fight well. It is enough to love the homeland.”
But, having gained consensus about the damaging and counterproductive effect of hatred in politics and the military, there is a growing demand to require an extreme form of another emotion - empathy.
The recent film "Eye in the Sky" portrays a possible outcome of extreme empathy: paralysis in political and military decision-making and disabling of soldiers. Whether this is true or not, Emile may know better, but it does seem amazingly disproportionate compared to the aerial bombing campaigns of 70 years ago.
I would suggest that the emotions of hatred and of empathy are at odds with effective political and military action.
As Keegan put's it "the deliberate injection of emotion into an already highly emotive subject will seriously hinder, if not indeed altogether defeat, the aim of officer training. That aim, which Western armies have achieved with remarkably consistent success during the 200 years in which formal military education has been carried on, is to reduce the conduct of war to a set of rules and a system of procedures – and thereby make orderly and rational what is essentially chaotic and instinctive."
Citizens in a free society are free to explore all action other than that specifically prohibited i.e. they have freedom to innovate within the law. (This freedom is rapidly disappearing in the "nanny state" but that question is for another day).
The military should have a similar freedom of action (and innovation) within the "laws of war".
But humans are contrary creatures.
Whether it is through drone strikes, aerial bombing, shooting a soldier, or topping one's parents to get the inheritance, killing dispassionately as a technical or strategic option in the absence of hatred - or indeed any emotion - is even more shocking to many people.
Hate is a powerful but very understandable human emotion. Legal systems around the world (in my view mistakenly) accept the emotional state of the killer as a modifier of consequences of an act.
The most extreme example of this is defensive homicide where a murder can be justified on the basis of fear of an imagined assault or a repeat of a past assault.
The emotions at play in these extreme circumstances include differing degrees of hatred, but our legal systems seem to accept human emotion as a partial justification for killing our enemies.
On the other hand, to kill one's enemies without hate can seem inhuman.
It is a paradox, that dispassionate slaughter is often more shocking than the same act fuelled by passionate hatred. When Islamist children calmly and methodically slaughter, there seems a calmness about their work which seems inconsistent with the arousal we might accept as at least a partial explanation for such acts. When bombs are dropped on camps and towns, the pilots exhibit a similar composure.
In conclusion, I completely agree that hatred should never be policy. When it arises within individuals, it should be seen as understandable, but regrettable. The expression of emotion in any open society should never criminalised, but should be openly condemned.
I also suggest that empathy should never be policy. When it arises within individuals, it should be seen as understandable, and laudatory, as long as it does not prevent the execution of duties.
In the exercise of political and military action, we should explore the meaning of justice and fairness.
Empathy is a valid influence within the individuals that compose these laws and policies, but is far to "emotive" to be built into these laws and policies.