I think a lot of people who say "I don't want to have children" base that on seeing the awful children other people raise. If you can identify the behaviour you don't like (screaming, making a mess, being generally unpleasant) then you can deal with it when they're your own. Most bad kids are just the product of bad parenting.
This is very much not the case for me - I generally like children, though not nearly as much as they like me, and am very good with them. Too good, because it leads to "you'll make a great mother" type comments, to which I always reply, either out loud or in my head, "or cool aunt." While I do like kids, I don't want to be around them for longer than a babysitting gig lasts, no matter how cool any specific child is. I have no desire to go through pregnancy, childbirth, caring for an infant or having a kid to care for after that.
The only scenario in which me having a kid is a happy thing in my head is the very specific future timeline in which I become a very good friend's egg donor, visit every so often and only ever get more involved than that when the kid's old enough to have conversations - also, this involvement does not extend to me having to do any heavy-lifting raising of the kid - I just take her places sometimes, show her to my family and teach her valuable lessons about life. (It's always a she. I guess if the child was born male, I'd just be like, well, I can't have a Ya-Ya Sisterhood of secrets with THAT. Seeya!
) And the reason my egg is even used instead of a more convenient arrangement where I befriend a niece or other child? Just so I can be like, "There, I've passed on my genes, now STFU EVERYONE." So basically, this particular subset of daydreams isn't about me having a kid - it's about me imagining a way to refuse to do what society/my family wants me to do with my uterus/life while never being penalized for it. "Look, I'm involved in her life! I brought her to dinner! I totes did the kid thing so
leave me alone."
So yeah, it's ridiculously late and I may have rambled or may have made sense, I don't really know, but the point is: I like kids but do not want any of my own. I face annoying pressure to (and patronizing insistence that, as being female removes my say in all matters, I WILL) change my mind about this when I get older. I keep seeing media be all "every woman wants children or HATES AND FEARS THEM" and as a result will idly make up futures in my mind every once in awhile where I can be off the hook for not working how I'm "supposed to." I therefore would like to refute the assumption that people who don't want kids just think they're all "bad kids" judging by some observed bad behavior. (Not saying you were making that generalization about ALL people who don't want kids, just have to address it. You are awesome, BTW, for not prescribing your choices as The One Right Way for everyone else.) It's quite possible to find kids silly and fun rather than thinking they're screaming poop machines and still have no desire to raise one!