I read a book called No kid! 40 reasons for not having children The best reason was that if your kid says you molested her/him sexually, you're pretty much guilty until proven innocent. A German woman killed herself in prison after being wrongfully found guilty of molesting her kid. Afterwards, it was revealed that nothing had happened.
So if you don't want to have kids, that's a pretty good reason to stand by that decision.
I think - and I'm not sure about this, mind you - that people who want to have kids imagine that taking care of your littl'uns will mostly consist of cooking for them, hearing them say "I love you, mom", goodnight hugs, and other loveliness like that, and aren't really aware of all the unpleasantness that parents have to endure.