One of my reasons for being childfree is that despite my very loving parents, I found it hard being a child: not understanding the world, being bullied, not fitting in well, always having to do what grown ups say. I often feel that I would not want to put someone through all that; the world feels like an increasingly hostile place to bring children into. I also feel that I have earned my adult independence by living through childhood, and have no intention of giving it up any time soon.
As for those who might say "childhood is so unfettered - you can play games, run around without a care in the world..." I actually feel I can do this more as an adult! As a child I thought playtime was always interrupted by having to go to bed when the grown ups say, to school, to church, you should be doing homework instead, etc. Whenever you did something fun as a child, you had to write about it afterwards. As an adult, you can set these "rules" yourself; and it's easier to anticipate them when they are set by someone else.
Interestingly, both my parents had older siblings who were childfree - as an oldest myself, I seem to be carrying on this tradition.
Having said all that, after seven years of being together, it seems that we do in a way feel a need to have a certain family "structure": we got married so as to have a sense of security, and we usually are up in the day and asleep at night - although we had loads of nights out in our early days, now we see them as disruptive to our routine. We are certainly not as "spontaneous" as we were seven years ago; we have developed annual routines of going to certain places, visiting certain people, and it feels very odd doing something different. Activities are usually planned and written in the diary a few days in advance, as they might be in a busy family household. So although we have absolutely no intention of having children, we almost structure our lives as if we did.