But surely it is good to kill sometimes. To kill disease-spreading insects, for example, or someone who is going to kill you?
It might be good for you but what about that thing or that person? They wish to live just as you do. When you decide to kill a disease-spreading insect, your intention is perhaps a mixture of self-concern (good) and revulsion (bad). The act will benefit yourself (good) but obviously it will not benefit that creature (bad). So at times it may be necessary to kill but it is never wholly good.
You Buddhists are too concerned about ants and bugs.
Buddhists strive to develop a compassion that is undiscriminating and all-embracing. They see the world as a unified whole where each thing or creature has its place and function. They believe that before we destroy or upset nature's delicate balance, we should be very careful. Just look at those cultures where emphasis is on exploiting nature to the full, squeezing every last drop out of it without putting anything back, on conquering and subduing it. Nature has revolted. The very air is becoming poisoned, the rivers are polluted and dead, so many beautiful animal species are extinct, the slopes of the mountains are barren and eroded. Even the climate is changing. If people were a little less anxious to crush, destroy and kill, this terrible situation may not have arisen. We should all strive to develop a little more respect for life. And this is what the first precept is saying.