From the opinions of Buddhist teachers from various traditions which I have read, I would say that almost all who saw the need for some response involving the taking of life saw it as a "necessary evil" ... not as a path or goal in any positive sense. Sometimes we must break a Precept to keep a Precept. And given modern warfare, most of the teachers were aware that this might include the unavoidable taking of civilian and other "non-combatant" lives in order to save a much greater number of lives.
I believe that the following responses, some by the Dalai Lama, are representative of the diversity of opinion.
(the comments which follow are also very interesting)
Thich Nhat Hanh may have been most representative of the "any violent response only leads to increased violence" opinion ...
The Buddha also seems to have been of two minds on this. On the one hand, there are some writings in which he is framed to say that killing is never skillful.
On the other hand, in other Sutta he did seem to countenance a nation having an army for certain limited purposes, and its discreet use.
Almost all the Buddhist teachers I can think of (including me too, for what it is worth) would say that we must also bear all the Karmic consequences of our volitional words, thoughts and acts, no matter whether we had a "reason" for killing or not.
You may kill the cat, but you still likely have to pay the price in some way.
A Tibetan teacher (Chagdud Tulku) relates this famous Jataka legend about a previous incarnation of the Buddha ...
(In a previous life, the Buddha was Captain Compassionate Heart, sailing with 500 merchants. An evil pirate, Dung Thungchen (Blackspear) appeared, threatening to kill them all. )The captain, a bodhisattva himself, saw the [pirate]'s murderous intention and realized this crime would result in eons of torment for the murderer. In his compassion, the captain was willing to take hellish torment upon himself by killing the man to prevent karmic suffering that would be infinity greater than the suffering of the murdered victims. The captain's compassion was impartial; his motivation was utterly selfless.
I am not sure about the effect of our Karma in lives to come ... but I do know that we likely will bear the effects of our actions in this life in some way. I have a friend, an ex-policeman, who had to kill someone in a perfectly necessary and justified act to save lives. Yet, my friend still carries that with him to this day.
No, taking lives is never a "good" thing.