In my opinion, it is largely because you might possibly change your mind at some point (you never know).Wounded Melody said:WHY are people like this?
My aunt used to be strongly against the notion of having kids (who would want to give up a happy and carefree lifestyle for a mewling, ever-hungry cabbage?) but now she happily has two of them.
People change their minds on lots of things throughout their lives, kids might be one of them (of course, they might also not. Again, everyone is different).
I think it's got more to do with 'keeping your options open' and 'being prepared in case you choose to' (or even accidentaly end up in that situation) than 'spreading misery' or 'because Da Man says so!'.