Self defense? Only on the battlefield? Only to achieve a ‘noble’ end?
There are a lot of things one can conclude from the ‘temporary’ nature of life (we know of several species whose sole cause of death is ‘eaten by predator’ or ‘died in an accident’ so life is not neccesarily temporary) and the buddhist interpretation seems to be a bit defeatist to me. “Life is short so I may as well throw it away” would have gotten humanity extinct at several points in history. If all life lived according to this mindset nature would be imbalanced and collapse immediately. Why should the deer rum from the wolves? Why should the rabbit from the fox? Without a drive to survive life would not have evolved past the microbial stage because there would have been no selection bias favoring individual genetic traits. As a result no single trait would get popular enough to get life out of the microbial stage. Now there can be a discussion about whether or not life should have evolved but that’s on another page entirely.
You cannot reason that life shouldn’t have evolved because any argument you can make is thanks to the fact that it evolved.