People who say it's dangerous and selfish are afraid of losing you. Yes, it's dangerous. Is it selfish? I don't know to be honest. But none of us get out of this life alive. My father passed away at age 45 (22 years ago today, actually) - he died of MND. My cousin passed away a couple of years ago, aged 34 - cancer. People die young all the time, and it's tragic, and awful, and loved ones are left angry and feeling cheated. I suppose it would feel a whole lot worse if they died of something "avoidable". But we aren't here to simply avoid risks, avoid doing something just because it might kill us. Of the people calling you selfish, how many smoke, or drink, or are over-weight, or drive a car in the rain/ice, or cross the road whilst distracted, drive when tired, drive a bit faster when late for work, or do a million other socially-acceptable things that are increasing the risk of death (no matter how small the increase)?
I have a child, and I ride a bike. I've ridden since I was 19. I learned to ride before I ever learned to drive. Riding a bike is not usually about transportation - it's a passion. I've been called selfish, but I just don't care. The people closest to me know that I'm not a loony rider - if I die on the bike it'll be an accident. Just that. And I would die doing something I love, living my life to the full.
However, I would say this to you. You are not an experienced rider (yet), so when people call you selfish and pretty much tell you that you're going to kill yourself - tell them not to fill your head with doubts, and stripping you of your confidence. You don't need to hear their voices filling your mind when you're riding your bike.
Best of luck to you, enjoy your bike,
xx