What do people mean by selfish when it comes to teen pregnancy?

This my sound like im a dumb person, but im not. I just dont get what people mean by "selfish" when teens are having babies. In my opinion i think its a wonderful idea as long as you're ready for a baby. I want a baby and im ready and im 16, and then someone goes off on me telling me how im not ready and that its a selfish thing for me to do. im homeschooled, i have a job, i have ALL the time in the world for one. Im also a responsible person. sooo ya tell me please.