On the one hand, hate could be seen as a source of evil deeds and thoughts, a purely counter-productive emotion. Yet on the other hand, hate could be viewed as a tool with which to motivate the elimination of injustices, whereby it becomes an extremely powerful, potentially productive emotion.
While a world of pure love would lack injustice, such a world does not yet exist.... Therefore, we must combat such injustices - and love is not often viewed as an emotion conducive to combat.
I don't label myself "Christian," but I very much revere the esoteric teachings of the Master Jesus. Fortunately, some of his quoted lessons were more on-the-surface, such at this one:
Love the sinner, but hate the sin.
When hate is viewed in this context, I think that it's worthwhile in some fashion. But I also think that what you think about, you become. So if you focus on hate--even the "justifiable"/"righteous" kind--it will still consume you over time; thus, it's much better to focus on qualities that you love about a thing, person or situation. And if you can't find something to love about it/him/her, then it's time to set your sights (thoughts) elsewhere.
With regards to love not being conducive to combat, I think that it eradicates the need for it (when employed properly, that is).
I believe it boils down to intent. If one is using hate for selfish reasons and personal gain (the sort of hate that bhaktajan describes) than it serves no greater purpose. However, if one focuses hatred towards evil, then it may have its uses.
I don't disagree with these points, but I still contend that one is better off setting his/her focus on love, rather than hate--even the justified kind. Be angry with the action, not the one who committed it. Use the feeling of hate as a momentary catalyst that spurs you to a greater action; do not wallow in it.
...I do not believe that love can overcome hate on the battlefield. Yet it is also my opinion that fighting fire with fire will only generate a more intense blaze.
When faced with a literal battle scene, I think that it's necessary to fight. But don't do it with hate/malice in your heart. Do it because you believe that it's your duty to protect--especially others and/or your country.
As for "fighting fire with fire," I think that such a mentality leads to strong karmic ties (and
not in a good way).