I don't have any children yet, but I do plan on having them someday. However, I don't believe everyone should have kids. In fact, I don't think a LOT of people should have kids. Most people feel they are "obligated" to procreate... like they are just following suit. Some people clearly are not parent material.
Why do I want kids? It's all about love, learning, and teaching. Having a family to care for, to spend time with, to teach things to, to go through life with is what's most important in life. At least to me. I want to teach things to my children that I wished I learned earlier in life and I want my kids to carry on my messages of unconditional love and helping others.
I don't have much experience with children... I'm an only child myself, but I feel I would make a good mother; even knowing ahead of time I will make a ton of mistakes a long the way and it won't be easy. I will try the best I can though.
Some people don't plan on being parents when it happens... but there's a difference between an accident and a surprise. If anyone feels they aren't ready for kids or don't want them etc... then please, by all means... use the technology science offers.
I believe bringing a child into this world is the biggest commitment you will ever make. If you can't make a commitment to your partner, think twice before committing to co-parenting with them. Children need a mother and father in their life... and there's too many people who put their wants and needs ahead of what's best for a child.
Anyway, maybe that's my natural instinct talking... but that's the best explaination I have for wanting to have children.