For me, I would say that having a child slowly began the process of me caring for someone else more than I cared for myself. It brought about a level of responsibility that hadn't been there before. It changed my world view quite a bit. Also it was fascinating to be on the other side of a lot of discussions, now as the parent as opposed to being the child/young adult.

So i've had a hard time lately, and the first thing that has truly made feel good in a few months is being around my niece and nephew a few days now.

Can you imagine if sex was very painful all the time? Humans would have gone extinct a long time ago. 

The general reason is to prolong the survival of our species. At the individual and societal levels, we manufactured different more immediate reasons for achieving that general reasons.
For many people and societies, it varies, but here are some decent reasons people have and raise children:

1. Pass a legacy. Along with ritual and tradition, legacy is a reason our life has some meaning. Without these things, we'd all be nihilistic emo wanderers with no purpose since the reality of our insignificance in this vast universe is depressing. The idea of keeping ourselves alive and passing it on to a new generation is comforting.

2. Share a relationship with someone at a level that can't be easily replicated by just meeting people. You know how there is just an instant love for many parents (most I would say despite all the terrible things happening in the news, because most animals are wired to want to care for their offspring in order to survive as a species). There are literal chemical reactions going on in our brain when skin to skin contact occurs between child and parent (yes, both mother and dad). And down the line, the relationship only strengthens as one party needs so much in order to grow while the other has all the responsibilities of nurturing that child. They can't help but have a relationship that is defined differently than every other kind you will ever have. It's kinda the cutest parasitic relationship you'll ever see.

3. It feeds the ego. A lot of people love themselves and would like to see themselves in another human being (not talking about sex, get your mind out of the gutter). Seeing that mirror image or even a few features makes a person feel great.

4. Some people are naturally nurturers. Whether it's pets or children or whatever, some people want to share their love with someone they can nurture and kids are perfect for that.

I guess that's all I got off the top of my head. And these aren't necessarily reasons why I would want a child. Just that I am aware of how some other people think. I'm sure a lot of people who have even more different reasons.

As a parent, for me this question is as valid as "what's the point of falling in love". I could try to come up with some valid scientific answer, but the truth is that you won't really know until you see your first born. It's like explaining the beauty of the mountains, just by looking at the picture. You can't really do that. You have to experience it yourself.

I guess I couldn't explain it better then Robin Williams in "Good Will Hunting". https://www.youtube.com/watch?v=qM-gZintWDc

Playing in the mud can in very rare instances lead to pregnancy. However the intention in those circumstances has nothing to do with procreation. Just because we slap a similar term within how we label the act, doesn't make them the same thing. It can also be argued whether nature intended on those acts being a natural way of life, or if they are mostly a harmless byproduct. What you can't argue is that sex in it's procreation act is clearly meant to be intended and natural.

What? :o 

Nice catch. 'Playing in the mud', not playing in the mud.

I got what you meant, I wasn't correcting you. 

I'm wondering how you can get pregnant from anal? I mean, I am a firm believer that anything can happen, but that sounds just incredible (in the "strange" way not in the "awesome" way)! I've never heard that before, sounds more like a meme in South Park than reality. 

Looks like I'll have to get Henqirue tested .....

Well explaining it I would have to assume isn't something for a thread in this section, so it can be googled if you really want to know, but obviously that's not possible between two naturally physically born males or females, which is exactly why genders exist in humans. However between opposite genders, there is a very real yet minuscule possibility.