@Quatl,
To me, the difference between good and evil relies upon which is greater...the loss or the gain?
But. Does that make it right to kill someone that annoys you if you know you won't get caught just because the gain for you is greater then the loss?
I think not. So, that makes me rephrase it to the gain/loss of the whole society/species, depending on your views. I prefer to say species for myself. I'd like to think that people should be working for a common good, although one person's view on what is the "common good" is probably very different from another person's view on it. If it weren't, we probably wouldn't have way.
If more people will benefit from something then suffer, then I feel that it's the right thing to do.
If more people will suffer, then it seems wrong to me, no matter who the sufferer is, whether it be a rapist or a murderer, or a close friend.
Because we can't forsee the future, sometimes we don't know whether something will be "right" or "wrong" in loss/gain type terms. That's when moral questions arise. In theory, it should be possible to find ways that stay within the boundaries of right by doing something that helps many people and doesn't harm the perpetrator so much, assuming there is one; Don't we have jails so we don't take human life, an act typically considered evil?
Then again, there is the limiting factor I put in before by saying the human species...not animal, or anything else.
How much is an animal life worth?
To me, an animal should never suffer because they are much more pure and innocent then people. Therefore, assuming that anything that would cause them to suffer would be wrong, I put some store in how much the animal is loved, used, or how much it gives to the environment that we need to survive.