Ok, so about the people who don't want kids:
Where do you think you'll see yourself in 20, 30 years? When you're 50 or 60 or something. Will you still be having the wild lifestyle you're enjoying now? Going out, meeting people? Having unlimited, unprotected, hot steaming SEX? No. So what will you have left? Nothing. Your husband/wife will be old and unattractive, you can't make friends easily.
I'm a hair from 30, and my fiance turns 39 this weekend. My wild, no offspring lifestyle means sleeping late occasionally on weekends, a lot of birdwatching, reading books and playing games in the evening, and cooking up good food in my kitchen. My near-term aspirations after my wedding in a couple of weeks are to repaint a few rooms of my house, find a regular bridge partner to get back into the ACBL duplicate matchpoint scene (even if it means tracking down an old buddy and playing online), shoring up my baking capabilities, buying some stupid expensive sim gaming PC accessories and playing some PC sims, and reading some mythology and history books that were recommended to me by a friend.
Not everyone who doesn't want kids lives an action packed life. I'm extremely domesticated, as you can see, but I don't want kids because it would get in the way of all those things, which I view as more important than childrearing. My fiance has equally unambitious-but important to her-aspirations.
But if you made some babies, you would have these loving people that you would call your son or daughter. And they will nearly always cuddle up to you and say
I love you mommy/daddy 
Come the fuck on.
Once you are 50 or 60, those kids will be one of three things:
1) Living on their own, and, given our highly mobile and busy culture, you might talk on the phone with them every week or so and see them two or three times a year at most.
2) They are semi-successful, and live in your hometown because they went to college there and found a job there. You see them quite often.
3) They are failures and are still "finding their way", and you get to deal with them still living in your house after all these years.
The cuddle up years stop at like eight or nine, tops, btw. Soon after that they want as little to do with you as possible for a good decade before you can reform working relations again when they get into their twenties.
What is important and vital in life to some people isn't so important and vital to others. The different reactions, one way or another, in this thread is definitely proof of that.
