Such a personal choice. I have biological children 5&6 and an adopted 16 years old who joined our family at 14. I have a pretty demanding career and can tell you that being a parent is the hardest thing I've ever done. The best thing too. I always say my kids are not my whole life, but they are my priority. I think anyone who is insightful enough to know themselves and that they aren't ready to take on that priority is very brave and wise, and shouldn't we ashamed at all. Don't let lack of motherly instinct be your only deciding factor, many of us have felt that way... Even when our babies were first born. I remember looking at my daughter in the hospital and expecting this rush of joy and connection, instead I was like "who the eff is this person and what have I done?!"
This makes me think of how I have some family members who think that all you are is how you look, I wasn't worthy in their eyes because I was overweight. Ne'er mind that I was the first to graduate college in my family and went in to get advanced degrees and was a successful, kind person. Same thing with being a parent, not one thing defines you. You are you and magnificent- with or without children.