I don't want children, never have and never will, I say that with as much certainty as someone who has a desperate urge to procreate has. I am in my late 20s and have a partner I love with all my heart. While some people want to 'make something out of their love for their partner' (as my own mother eloquently described it), I do not want anything to take away from my relationship and children definitely affect relationships.
I disagree that people who have children or people who don't have children are more selfish than one another, and think the accusation of being selfish is a hurtful one regardless of the decision. I have been accused of being selfish because I don't want children, but there are so many ways to 'give back' such as volunteering, helping care for friend's children, helping care for elderly relatives etc. I have heard people say they want to have children for someone to look after them when they are old, or to 'fit in' which aren't very selfless reasons. Yes, having children involves many sacrifices but I am sure that there are many parents who wouldn't sacrifice the same things to look after a child that is not biologically their own. The 'selfish' thing could be argued to death but ultimately, people do what they want for their own reasons, each choice is selfish and selfless in equal measures and such a personal decision should not be questioned.
What really gets to me is people imposing their own choices onto me. I would NEVER question a friend's decision to have a child, even if I thought they weren't capable of bringing up another human being, yet the number of times I am told 'you'll change your mind' is astonishing, as if the decision not to have children isn't acceptable. It's not that I wouldn't make a good parent, I'm sure I would, but I have no desire to be a parent and am more repelled by babies than compelled by them. I find myself constantly having to justify my decision. I accept that people who have and want children make up the majority for whatever reason, and that they often fail to comprehend why people don't want children, just as I don't understand the 'urge' to have them. However, my decision is no more likely to change than theirs is. The day that not having children is acknowledged even half as much as the decision to have children will be a happy day indeed!
As someone who is probably older than most people on these threads, my advice would be stay true to yourself, try to discover what it is that you really want to do with your life whilst drowning out the voices of society and other people, and know that your choice is personal to you and someone else's might be completely different yet entirely as valid.