I always assume people who don't want kids feel the way I do about pets - i.e. that they are a massive drain on time, energy, resources and freedom for very little return. I know people who go gooey over horses/dogs/cats the way I do over my (and indeed other people's) children, when all I see is a big dumb smelly creature that wants and wants and wants, covers your home in hair, needs grooming, exercising and generally minding like a young child would with the additional down side that they are NEVER going to change.
Now I'm aware that there will be a load of dog/horse/cat lovers who will think I'm a sociopath 
now I don't think childfree people are; I just think we have different definitions of value and different things that make us fulfilled (which btw is not the same as being enraptured every single day, a solid week of fevers and D&V in a pre-verbal toddler isn't anyone's idea of fun!).
For me I think really fulfilment is about engagement. Some people are fully engaged by their careers, or their partners, or their education, or all sorts of other things that I enjoy but which never really 'hookee' me the way my child does. I am always engaged with being her mum. I never lose interest in it or wonder what the point of it all is really. And that makes me feel like a proper part of the world, when for much of my life I felt sort of off to one side and passing through, even when having a wonderful time. I don't want loads of kids (one more and I'll be done) because I want to remain that engaged and not diffuse it too much.
But I KNOW my way isn't the only way to feel that engagement; and other people get it by jumping off bridges or going to church or getting to the very top of their game professionally or snuggling with their schnauzer or working on a cure for cancer or running marathons or baking really, really fantastic cakes. Or many other things besides. And I know what I get out of having a kid isn't the reason everyone who has them has them, or everyone who enjoys them enjoys them.
I wish a thread like this could be a nice, positive, supportive one about the benefits and/or consolations of childfree living, instead of segueing into slagging off parents and implying they've made s terrible mistake. I appreciate this is childfree people kicking against the general cultural norm that children are "what you do" and those without are somehow lacking, but it's still pretty unkind.