I've never wanted children, and I really doubt that I ever will. It's a totally irrational choice people make not for themselves, but to fulfill a biological imperative which serves the purpose of the species (which, like all life, is to replicate indefinitely) at the expense of the individual.
Oh, certainly some people get rewards out of it. Again, mostly biological imperative thing. And yeah, I have a twinge of maternal instinct from time to time, but even then it's about what I could create rather than simply bringing a new life into the world for it's own sake. Even if that was a good reason for having a kid (which it's so totally not), and if things actually worked out the way I wanted, it wouldn't be worth the investment of time and money.
And that's what it's really all about to me, time and money. Children ruin your life for 18 years and nine months, and that's assuming everything goes well and they're not still living in your basement when they turn 30. And what do you get out of it? Love and affection? Probably. And maybe someone to pay for your retirement home when you're old, but that's a bad reason as it's much wiser to invest the tens of thousands of dollars a child costs and retire rich. Less risky, too, as children only sometimes turn out successfully. Some aren't inclined to financial success, and others are just lemons--autistic, sick, retarded, or otherwise natural losers.
Add in the fact that I'd be a terrible mother (for any of dozens of reasons, most of which boil down to the fact that I'm selfish and consider my needs to be paramount), and having children just seems like a bad idea. Bad for me, bad for them, bad for the world which doesn't need another dysfunctional person added to it.