The first word that comes to mind is 'cost.'
The second word is 'inability.'
The third would be 'impractical.'

Basically, it would cost too much, we aren't even able to put a man on mars at the moment, and putting 7 billion people under a dome on another planet or the moon just isn't practical right now.

If we lived ON a big dome on either planet we would suffocate, but maybe we could live in the big dome.

they are planning to build a human settlement on mars by 2023. have a look at this [ Register or Signin to view external links. ]

Because it's a useless investment. Literally billions, if not trillions of dollars to afford a dome big enough for maybe the size of a US city.

It would be useless and it would kill us. Unless we had sufficient ways of ventilating all of the carbon that we breath out, there would be no way to survive especially since both the Moon and Mars are much smaller than Earth. Although this would be cool, this could happen in the future or even better we'd find a planet with a suitable atmosphere with all of the essential elements.

It would be a dream to go to mars but I guess only the rich and famous will be able to go in my lifetime.

Very interesting watch. I saw this about a week ago.

the reason we cannot live on the moon is due to the amount of helium 3 that is up there and the US government doesnt want joe public to know they have been mining the moons surface for over 40 years... why has there been no more moon missions since the cold war?? why are we only orbiting the moon via a space station?? apparently an alien moon base is on the darkside called LUNA, in the 60`s mankind had the vision of colonizing the celestial body to make use of and make our new home.. we had so many grand ideas and plans the suddenly we resort to a quick timed mission of collecting a few moon rocks then straight back to earth, WHY?? the goverments of the world will not tell the ordinary man what is up there or why we wont go back... HELIUM 3 is a true resource - google it, HELIUM 3 is also 100 times more powerful than our nuclear fission... 1 tonne of this compound would be enough to supply a country, the size of america for energy for well over a thousand years.. its also the next step in humans being able to travel greater distances.. on earth now we are facing a critical time in history as we try to step away from the use of primitive fuels and energy supplies (gas, coal, electricity, nuclear power).. for the continuality of the human race we must evolve so therefore does our consumption of energy... helium 3 is that next step and the value to a said goverment ( THE UNITED STATES) infinate... controlling such a resource could effectively change the planet and also become extremely profitable for the man who holds all the power (HELIUM3 + UNITED STATES GOVERNMENT = NEW WORLD ORDER).... thank you