I know so many people who have kids now, and the more time I spend around children, the more I decide it's not for me. When my mother had her surprise baby at 45, (now a 5-year-old), and when my sister had her baby 2 years ago, I was frequently chastised for really not knowing what to do. I know how to hold a baby correctly, how to prepare the bottle/feed them, change the diapers, but there's apparently a lot more than that, and I don't "get" it like everyone else does.
My late husband and I discussed at length how it wouldn't be fair to the kid if we had one. We each have so many health problems that would be passed on, that we just didn't want to put another human through after experiencing firsthand. We also discussed the terrible shape that my back is in, and how it's likely that I couldn't physically stand pregnancy. I'm in enough pain on a daily basis, and have had to leave work early due to being in too much pain to SEE. Add the weight and stress of pregancy - I'd be a useless invalid the whole time, and I just can't accept that. I have this work ethic thing, I don't even like it when I get paid to sit around reading or knitting because we're out of work. My absolute lack of maternal instinct was a factor, as well.
Speaking of that - my sister and my nephew are currently staying with me while my sister job hunts. Apparently, I have a good "Mommy voice", while she tends to yell or screech more frequently. Aside from the voice, I don't know what I'm doing, I really don't. I just copy her if I need to discipline him, like when he jumped on my cat. But the more time I spend with children, the more I know I just don't have the patience for it, or the ability to deal with most of it. I can barely handle cats and plants, I should not ever have a child. I can't clean up puke, I'll add to it. I can't clean up poop, I'll puke. I can't even hear someone puke, or I'll join them.
I occasionally hear mothers talk about what an amazing experience I'm missing out on. It may very well be amazing for you, I'll take your word for it. But it sure wasn't for my mother, my sisters and I were heathen demon children. Some people should have kids, and some shouldn't. I feel that I fall in the "shouldn't" category, and will certainly refrain.