Any thoughts, speech or actions that are rooted in greed, hatred and delusion and lead us away from enlightenment are bad and any thoughts, speech or actions that are rooted in giving, love and wisdom and thus help clear the way to enlightenment are good.
To know what is right and wrong in god-centered religions, all you need to do is to do as you are told. In a human-centered religion like Buddhism, to know what is right or wrong, you have to develop a self-awareness and self-understanding. Ethics based on understanding are always stronger than those that are a response to a command. So to know what is right and wrong, Buddhists look at three things:
1.) the intention
2.) the effect the act will have upon oneself
3.) the effect it will have upon others
If the intention is good - based in giving, love and wisdom - if it helps myself -helps me to be more giving, more loving and wiser - and help others - helps them to be more giving, more loving and wiser - then my deeds and actions are wholesome, good and moral.
This gets a bit complicated – at least it does in my mind. There are many variations of actions, intentions and results:
1). Sometimes I act with the best of intentions, but it may not benefit either myself or others.
2.) Sometimes my intentions are far from good, but my action helps others anyway.
3.) Sometimes I act out of good intentions and my acts help me but perhaps cause some distress to others.
In such cases, my actions are mixed - a mixture of good and not-so-good. When intentions are bad and the action helps neither myself or others, such an action is bad. And when my intention is good and my action benefits both myself and others, then the deed is wholly good.
The Five Precepts are the basis of Buddhist morality. The first precept is to avoid killing or harming living beings. The second is to avoid stealing, the third is to avoid sexual misconduct, the fourth is to avoid lying and the fifth is to avoid alcohol and other intoxicating drugs.
What about Killing?
The question of killing something, like a disease spreading insect, often comes up – how can that fit into the precept of avoiding killing or harming other living beings? Wouldn’t it be a good thing to kill insects that spread diseases to human beings? Well, it might be good for you, but what about the insect? It wants to live as much as we do. So when we decide to kill a disease spreading insect, our intention is a mixture of self-concern – good – and revulsion – bad. The act will benefit us, but obviously it will not be beneficial to the insect. At times, it may become necessary to kill, but to kill is never wholly good.
Buddhists strive to develop a compassion that is unbiased and all-embracing. They see the world as a unified whole, where each thing has its place and function. They believe that before we destroy or upset the balance of nature, we should be very careful.
Look at cultures where the emphasis is on exploiting nature to the fullest, squeezing every last drop out of it without putting anything back - conquering and subduing. Nature has revolted. The very air is poisoned, the rivers are polluted and dead, so many beautiful animal species are extinct, gone forever. Slopes of the mountains are 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.
This is what the first precept is saying.