I would say that at least half of all people who become parents did not have a huge , overwhelming drive to have them. They had a "when the time is right, maybe" sort of level of passion. I know I did. I had my first at 32, second at 38, and we still didn't think the "time was right", but it happened.
But, no horse could have brought me the personal development that motherhood has. I know that people say that their horses,dogs, or other pet are their "children", but it is not the same.
I sometimes do wish I could sell my children, or at least the older one, but when I think of how important my familial relations are to my siblings and parents, I think of how important it is to keep that human chain going.
True, not everyone should be a parent, and since it does not have the temporary nature of pet/horse ownership, it should not be taken on lightly. But, do not worry that you do not have a drving passion to have a baby. Most of us parents didnt, at the time, but we are glad we did.