Yeah, I think everyone knows someone who didn't live up to their potential or made some poor decisions and are stuck doing something they hate for a living. And there are plenty of people who get the good job (doctor, lawyer, professional...) and hate it. No one can determine your future for you.
I don't think anyone who has advised him to think twice before making the leap is saying it's all about money. In fact, if you read back a bit I tell him that a 10 year plan should be more than feasible if he is willing to put in the hard work to make it happen. Roger also gave some great advice about considering different business ideas if he wants to be self employed.
Many people think that business ownership is some sort of freedom or euphoria. For some it is. For many others, they do not have the skills nor drive to make it happen. On a forum like this, there is no way to know whether the OP is going to start the next Brinkman or is going to be the next guy to list all his equipment for sale because he couldn't make it a year later.
Also, another point to consider is his family status. He has a wife and young child that solely depend on him for food, water, shelter, clothing, etc. Is having a family and starting a business form scratch impossible? Of course not! But it would be unwise to give the same advice to OP as to a single guy/gal without a care in the world. When a person decides to get married and start a family, he/she is adding extra responsibility that must be considered when making career and life altering decisions.
People have given some thoughtful advice to OP. It is easy to say, "You only live once, shoot for the moon!" "Who cares if it doesn't work out, you can always start another business/job!" "People are trying to hold you back!" Quotes like these could go on for pages. But people who give that advice usually aren't on the other side when said person's new business ends up failing. It isn't easy to watch people who own their own business struggle and fail in this tough economy.