Humans lived and thrived in what is now the United States for at least 15,000 years before the European colonizers arrived.
Mars is obviously fundamentally different. Despite what Elon likes to portray, “terraforming” Mars may not be possible and the colonists will always have to live in enclosed pressurized structures, donning suits for “outside” excursions. But achieving that is just an engineering problem. And humans are amazingly adaptable to new environments.
Every place that humans have effectively colonized has had air at around 1 ATM, has had abundant potable water, has had plants and animals suitable for food and clothing. Mars has an atmosphere 1% as thick as earths, it has no liquid surface water, only some ground water and water tied up in minerals, and all of it saturated with deadly perchlorates, and it has nothing edible. There is no suitable analogy to express how much more hostile Mars is than the most hostile environment on Earth.
Humans have adapted to a very narrow range of temperatures, and they've adapted to a change in food sources. But notably, colonies get established because people want to get away from enemies or despotic rulers, or they get established because their home nation wants the resources in a far-away place.
There is nothing on Mars that colonists could use to pay the costs of getting there and establishing themselves. They would need supplies from earth for at least a hundred years, and probably forever, and there's nothing on Mars that would be worth more on Earth than the cost of transportation to get it here. They'd have no way to pay for anything they'd need.
You are very sure of your conclusions. Just 150 years ago, “experts” confidently stated that “flying machines” were impossible. Rockets to orbit were just a Jules Verne fantasy, which no one took seriously.
"They laughed at Fulton" is not a valid argument. The vast majority of times that experts have said something was impossible, it was.
And FWIW, nobody with any scientific credibility said that flying machines were impossible. What they said was that a flying machine would require a motor with a better power-to-weight ratio than yet existed. And they didn't say that rockets to orbit were impossible. They said that they would have to burn X amount of fuel in Y amount of time, which was not technologically feasible until the 1950's.
Of course ”artificial habitats” will be required on other planets. Modern humans overwhelmingly prefer to live in “artificial habitats” here on Earth; they are commonly known as “houses”. Many people spend the majority of their lives inside; their home, work place, car. Their time “outside” is just a small fraction of each day.
And people famously become stir crazy when they are unable to go outside and breathe fresh air. Prospectors snowed in for the winter and convicts held in solitary confinement go bonkers. The lack of an effective atmosphere and magnetosphere will require settlers on Mars to spend all their time underground, and cosmic rays will severely limit the amount of time anybody can go outside in a space suit. A Mars habitat will be a prison with no exercise yard. If we want to spend more money than it would take to eliminate poverty world-wide we can establish a research station where people commit to a year on Mars, plus transit time. But there's nothing there that could pay for a self-sustaining colony. There is no possible resource on Mars that would be worth enough on Earth to pay for shipping it back. And the colonists would have access to extremely limited medical care. Drugs would take months to get there, diagnostic machines would be unavailable. You'd have medical care equivalent to a 19th-century country doctor with his black bag.
Space suits will of course be needed. They exist today, and they can certainly be improved upon. That’s an engineering problem, not an unsurmountable barrier.
There will be many Martian colonists who will gladly accept living in pressurized structures, and their children will consider it normal.
What we can accomplish over just the next century or two is hard to envision now. When I am up in my local mountains I often look out over the metropolitan area where I live and think about how none of the human structures that now cover the land existed just 180 years ago. There were thousands of people here back then and they had constructed dwellings, but from my high up vantage point none of them were likely visible back then.
The pace of change is accelerating. No one reading this today will be alive in 2132 but it would be short-sighted to assume humans will not be permanently living off Earth by that time.
And all those structures were built under an open sky of breathable air, on land with potable water, in country capable of producing food.
One more note on "terraforming": Nowhere in the history of humanity have people succeeded in POSITIVE large-scale changes to the environment. We only make it worse. If we cannot even keep the Earth habitable, how are we supposed to make Mars habitable?
A research station on Mars is possible, at an obscene cost. A self-sustaining colony is not.
