I'm post-menopausal, and I'm someone who opted out, after being very conflicted for years and desperately worried that I would regret not having kids. But I couldn't deny that the work, worry, and expense of it all sounded very unappealing, even though I could also see the benefits of having kids. My husband felt very similar. Ultimately, we decided that it's best to regret NOT having kids than regret having them.
Several posters have mentioned loneliness and a lack of meaning without kids. One said that life would be very solitary, another said that going to other countries would be a bit meh without kids, etc. I'd like to discuss these points.
Well, they're not wrong. Even someone like me, who is very happy with their own company and who really didn't like the idea of the domestic load that comes with kids, it IS a bit lonely not to have them. Even when I was still married, sometimes we'd go away on our own and it did seem a bit empty without kids. Also, as an adult, life is more solitary if you don't have the built-in bustle and noise of having kids in the house.
But. For all that, I think it was the right decision. I still wouldn't want to take on all the work, worry, and expense, and I think if you're not young enough to be living at home with your parents, or if you are not a parent yourself with children living in the house - in other words, you're not living in a family unit - life IS a bit lonely.
One thing that not having kids has given me is the time and focus to look outwards, to really see the other people in my life, to volunteer, to look at the world around me and to wonder at it and take pleasure in its parts that aren't to do with family. It's such a beautiful world and there are so many ways to live your life. If you don't have built-in companions in the shape of a family, you do have to work harder to find meaning, but it can be done, and a life lived on your own terms is meaningful in itself and can be its own joy.