Is it selfish to have only one child?

My son is 14 months old and before he was born as well as after, I decided he would be my one and only. I am perfectly happy with my baby boy, and look forward to spoiling him and giving him my undivided attention. But my husband and family have a strong opinion about a single child. They say that a single child will turn out to be a brat if there is nobody else to share with. I'm not sure.

I have a question: There are a lot of women that would, infact, risk their health for the chance to have children, but I am not one of them. A girlfriend of mine thinks I am being incredibly selfish, what is your HONEST opinion?