There's one. Run!
If you're lucky enough to one day make it to your 40s without having kids, you'll find that there's a certain segment of the population - called "parents" - who will demand an explanation of you.
When they do, sit back, smile, and use one of my stock lines:
1. I chose freedom.
2. I believe the position of whining bald baby has already been filled in my household.
3. I'm afraid they'd play with my toys.
4. I'm like Tarzan; with one yell, all of my genetic material comes back to help me fight the evil doers.
5. Can't afford to, thanks to all of the education taxes I pay for yours.
6. I can't hear you with this condom pulled over my head.
7. In order to have kids, you must have at some point had sex.
8. I do not want anything that Celine Dion wants.
9. Doesn't the world already have enough snot?
10. I'm waiting until I'm 80 to have them - no one expects you to change a dirty diaper when you're wearing one.