At the expense of what family? The hypothetical one which I am purposely not creating? I'm glad that it's worked out well for you (really), but you need to recognize that, contrary to what people want to believe, parenthood and happiness are not synonymous. You look at my life and see empty houses (nevermind that I live with a bunch of fun, like-minded people); I look at yours and see sleep deprivation, debt, stress, loss of the ability to travel and develop myself personally--basically the end of everything I enjoy. Other than conventional wisdom, is there anything to suggest that your life is "immense and awesome", while mine must be empty and sad? For my part, I see a litany of studies suggesting that people like me are, on average, actually a lot happier (http://nymag.com/news/features/67024/).
I would never be so smug as to insinuate that you made the wrong choice. But it's not your place to make face_plains at me, either.
If you were to marry and have kids, you would likely argue the same points about it being the greatest experience of your life. However, you would only feel that way because your memory of your past bachelor life would be distorted by the joy that your new settled life has brought you.
So I think you're both right. :)
You can have a very happy life with or without children. My wife and I waited until our late 30's to have our daughter. We were happy before and we're happy now. If we decided not to have a child we would have been happy. Your list of downsides to having a family are accurate with the exception of "develop myself personally". It depends on what you mean by developing yourself. If you mean being able to study interesting subjects, e.g. take foreign language classes/study cooking/etc., then there's some truth to it. With a child, you have to pick and choose what you study based on having a less flexible schedule. But, developing oneself isn't limited to that. My daughter causes me to learn patience, empathy, and selflessness far beyond what I could have learned without her. It's a matter of not having a choice to do otherwise.
As for the other side of developing oneself, she and I will be studying martial arts and piano together. Not bad.
Enjoy your life whatever your choice. You're the only one in control of your happiness.