People who left were able to start fresh.
They were able to tap into a different resource base.
We can think of the world as your parents house and the unfinished basement as the Gobi Desert.
What makes moving out better than living in your parents basement ? It is cheaper in your parents basement. It is tougher to move out, you have to do your laundry and maybe cook for yourself and landscape your new place. You would have enough room in your parents basement. Does your older brother have to remodel and live in your parents basement before you can move out ?
Strike out on your own.
Make an independent life for yourself.
We could keep densifying your parents house and people living in the house could get weapons that could easily blow up your parents house. If we spread out across the block and city then we would not kill each other as easily and we would have more room to stay out of each others way. If you have guns and grenades or matches in the same house it is very easy to take out the whole family. The families survivability is better in multiple houses. This is unrelated to how well different family members get along or whether some people have trouble keeping a job or being able to buy their own food and feed themselves.
re: Perfecting ourselves before leaving the earth ?
Is there some standard that we should be perfect before we leave our parents house ? Do we solve all of our problems before we leave ?
Does moving out mean that parents do not need to keep working on their problems. Don't you have to keep working on your own problems. Would staying under the same roof help solve the problems any faster ? Does it prove anything that you learn to not kill your parents and you learn to live together with them ?
In the solar system the earth gets one trillionth of the total solar energy emitted by the sun.
There are a lot more available resources in the solar system that we can utilize if we crack the cost of space nut.
Those who think no one will ever colonize space are in the same mould as "I am living in my parents basement and I am happy and it is better economically than moving out, I cannot imagine anyone moving out of their parents basement ever"
The "lets not colonizing space until we colonize the Gobi Desert fallacy or until we have no problems fallacy" is the same as "lets not move out of our parents house until our family problems are all gone and have remodeled every square inch fallacies".
Let me also repeat that short camping trips in the backyard do not count as serious attempts to leave home.
The easiest way to get people to want to leave home is to have an abusive set of parents or those who are too domineering "if you live under my roof then you have live by my rules". Eventually someone will want to leave even if the parents are nice and cool..
UPDATE: Further analysis of the analogy based on a comment by Shubber Ali.
The leaving your parents basement analogy was for indicating that sometimes we leave someplace even if it costs more to do so. This indicates a clear and common case where you go even if it costs more and is harder to do than staying.
Shubber brought up issues of 1) air 2) water 3) food 4) ease of access 5) gravity. For those issues we go back to the title of my article. You would have to find ways to bring water and food to the Gobi desert as well. You would have the cost of growing food. There is also the issue that China claims the Gobi desert. So if other countries tried to colonize the Gobi desert then they would need to follow the rules of the Chinese government. This matches up with the analogy of the basement (my house my rules).
Air can be brought and for certain places (moon, Mars) can be processed from local materials. Moon and Mars have gravity and a spinning space colony would have simulated gravity from centrifugal force.
To match the basement analogy to these situations more closely:
Leaving the basement, to a house that you have to build. You have to connect to the local water line or if you move out to a place with no utilities (like space currently) then you have to dig your own well (it costs more but it can be done), you have to build a septic tank, you may have to grow your food if there is no store nearby.
Another option is that you buy a big mobile home that has more ammenities with it. You could start growing some indoor plants before you leave home while the mobile home is parked in the driveway. thus it will be easier when you go to that new plot of land off of your parents property.
Those two examples, I just brought up are ways that I think we should use as part of a plan. We can build or send infrastructure into space first. Robotically built or inflated structures for gathering energy. Sending machines that process and pre-genrate lunar regolith for oxygen or from the Mars soil and atmosphere. Structures with aeroponics or hydroponics can be sent after the energy and air infrastructure has been established.
The mobile home analogy is that you make and launch something big. Something as close to project Orion as the public relations will let you get.