From what I have seen so far, people come to being childfree in one of several ways:
The early articulators have generally made the choice so long ago that they do not remember even making it - it has just always been that way for them. For the rest of us, though, the choice has to be made - but how?
The best way that I know of is to imagine your life as a childED person. Take a month, take two, take six. This is a major, MAJOR life decision, and should not be rushed. (If you feel that "I have to have a baby RIGHT NOW", you are in the grips of what is often called "baby rabies", and you, more than anyone, MUST take the time to truly think it over!)
Imagine how your life will be. Picture yourself daily with a child. See yourself doing all of the little (and not so little) things that a child needs.
When you feel that you have a good handle on this side of it, reverse it. Imagine yourself childFREE. You will never have a child. (Does reading that statement make you feel sick and scared, or relieved?)
Picture yourself daily with no children. What will you do with your life? Will you change careers? Change towns? Change relationships? How will you be?
It generally seems to happen that, given enough time for thought, the decision becomes clearer. If it does NOT, if you still feel "on the fence", I would gently suggest that you are actually childfree.
I do not believe that "well, sure, I could have a kid, I guess" is enough to make you decide to have one. There are many sacrifices and life changes involved in having children and raising them properly, and if you don't really care either way, I think you should choose not to have one.