"I would consider the Antarctic a scientific expedition and not a colony. A colony would have a full spectrum (in time) of humanity and be working towards self-sufficiency "

So, that's Ma, the little brat, and a goat?
:)

I think we need to start from the beginning and work forward.
Why are we doing anything in Space?
I think we can throw out the curious and wonder- because we could exploring the bottom of the ocean for that.
Security is a good reason.
Finding out about Earth: environmental forecast or say severe weather.
Global communication.
So, these are reasons for going into space, but they don't include Mars in the picture. Nor do they include our Moon. Though studying other worlds does help in understanding Earth.

Low cost energy needs?
Now, we are going through cheap energy reserves pretty quickly. In a world of ever increasing generation of wealth, a very key aspect is having a cheap energy costs. We have this increase in wealth because we aren't using animal power to grind wheat or move water. With technology which dependent of a cheap source of energy- one farmer can generate enough food for +100 people. Therefore people are not required to spend most of their day getting food- they do other things which are considered valuable which allows them to buy food.
But in a broader sense, cheap energy allows things which made and transported to be cheaper. If energy cost rise, this will have impact on entire economy. Currently coal can be used to generate electricity so it can sold profitably at wholesale at around $ .03 a kilowatt hour. If the cost of generating electricity were to increase so they had to instead charge $.30 per kw hr, you could easily pay more for electrical power than the cost renting or owning a house (house payments). Not only that, but everything would skyrocket in costs. And if you can lower the costs of electricity, then it generates more wealth. So if Space can offer a source of quanitity of continuous cheap energy then that would make a "world of difference". Now, of course at the moment the cost of getting energy from Space is hideously expense, but there is the potential of getting huge quantities of very cheap electrical power from Space.

Another aspect of Space is it allows long range Earth transportation at very fast speed- travel anywhere on Earth in about an hour. At moment this kind of transportation is also hideously expensive, but again it's possible to lower these cost to the point in which it could as cheap or cheaper than conventional airline travel. This actually easier to do than trying to get cost energy in space low enough to sell to an Earth market. It's about in order of scale of a billions of dollars compared to trillions of dollars- assuming money is spent wisely.

Anyways, if we are engaged in sub-orbital tourism and/or developing a market for electrical power in Space, I can easily see us extending our reach to the Moon and further out to Mars. If we continue the model of NASA charging around the solar system without including the step of the private sector building and controlling the required infrastructure to make Mars reachable to us "common folk" then Mars will never be colonized.