Not surprisingly, the basic evil of working against your our species survival gets complicated as you examine how to react or evaluate real world situations. Does that mean you should always have as many kids as you can? I think not, if also means that they will not survive to reproduce themselves, or that they will be in poor physical/mental condition due to scant resources and thus be less likely to be able to succeed at the complications of life themselves. Remember, in an evolutionary sense, it is not personal survival that counts, but the survival of offspring that can and will also reproduce successfully. In human cultures, especially more technical and dense (i.e., existing in high population densities), the complexity of the social "rules" take real effort and time to learn. Just look at how long it takes your average teenager to act like an adult for some hint of this. So having lots of children is often shortsighted, in a species survival sense. But by the same token, I can argue that choosing to have no children is generally a poor, and maybe even evil choice. If a biological evolutionary sense, you have become a zero. Indeed, by not allowing your genetic heritage to be spread into the future, you may very well be damaging the human species - a true evil. The problem with this logic is that it can lead to the political abuses of eugenics. I have no problem with eugenics as a personal choice, but a huge problem with eugenics as a government mandated program - or even something the government encourages. So, the only exceptions to doing evil by deciding not to have kids are 1) you determine that you are not fit, or 2) you determine that your value in a cultural/scientific/societal sense is so high that it more than negates the lack of offspring. The latter, of course, requires a very high opinion of not only yourself, but what you are accomplishing in life. And self evaluation is always suspect. The only true test of the second would be, I think, societal recognition.