Between childhood trauma and a dysfunctional family environment, I've always known I would be childfree by choice. I was another who felt resented by their mother, and was very aware of her jealousy even as a small child. She would always make comments like "I gave up my life to raise you, and I lost myself" etc...it was hard to feel like kids were wanted in her life, because she mostly focused on all the things she had to sacrifice once we came into the world. Once I was a teenager, and older, she seemed competitive with me, and when I would get an opportunity to do something, or have athletic success, it would always be about how "she never got the opportunity, or chance" or whatever...
Anyway, all of that to say I've always known that I would be childless, and a lot of it stems from never wanting to recreate that environment for a child. I'm not saying I would act in that way, but I wouldn't even want to risk the idea of feeling resentful, or like I missed out on something because I had children...I know how painful it was for me to hear/feel those sentiments from my mom, and it's affected me a lot now as an adult.
My other reasoning is really because I lived in a very sheltered, limited (by religion) upbringing, and only since I moved out, graduated college and moved as far away as possible have I felt like I'm becoming my own "real" person. There's so much of life I still want to experience, I'm overwhelmed by the possibilities and can't even imagine putting all of that on hold to create a new life that will be my sole focus for 18 years. I feel sad admitting this, but I was never happy, and never had fun as a kid. I always had this "weight of the world" feeling on my shoulders, even as young as 7 or 8. The first time I ever felt truly happy was learning to mountain bike at 21, and having SO much fun and realizing that I had found something that I was passionate and excited about. I called my mom and told her how much fun I had all weekend with friends, mountain biking and experiencing new things...and she said something like "it's good to have fun, but you're an adult, make sure you're focusing on being responsible." She couldn't (still can't) understand that I spend every weekend riding, camping, climbing mountains, skiing, doing all of these things that bring me immense joy in life. These experiences and passions are so fulfilling, and I feel so much joy that I didn't even realize was possible when I was a kid...it feels a little like making up for lost time growing up.
Anyway...that was a bit of rambling, but all that to say I'm childless by choice, and probably always will be. It's not the right choice for me, but I see so many of my friends becoming wonderful parents to these adorable little ones, and I appreciate that and respect that.