I've often wondered about this question. Excluding the people who accidentally fell pregnant or were raped, why DO people have kids? In the old days it was probably to help out with the farm work or the family business.
These days, couples are having less children and often delay having the first child till much later. Most people eventually get around to 'having kids'. Once again, why? I've heard people say that they want kids so that there will be somebody to look after them in their old age. What guarantee do they have that their kids will in fact do this? Of course, there are those who just love kids and always dreamed of having their own. If probed further, they usually don't know the specific reason WHY the children need to be their own. Why not just become a teacher and be surrounded by other people's kids all day long?
I believe this is truly one of those instinctive situations in life. There is no answer to the 'Why?'. I never thought about having a baby until sometime in early 2005. Then, out of nowhere, I just 'felt like it'. No rhyme or reason, I just felt like I wanted to be a mom. Seriously, it was literally an overnight thing. Richard used to be one of those people with no specific reason why he wanted kids but after we pondered on this question several times, and only after Aaron was born, he finally said "I think I wanted a child so that I could teach another person how to be a good human being". Well thats an answer that I like hearing! I still don't have an answer of my own but I'm glad that I didn't wait around till I thought of one.