Think back to the days when the United States of America belonged to the Indians. When the white people arrived dd they ask if they should be allowed to live in America? Did all the tribes cast a vote, yes or no? Too bad for all the Indians who voted no. What happened? Whether or not the Indians wanted the white people they settled anyway and look what you have today? Too many white chiefs and not enough Indians.
Just supposing there were life forms on Mars. Presumably people will eventually travel to Mars. The first thing they would have to do is round up all the Martians and place them on reservations. Bit by bit as Martian land was needed the Martians would be forced off those reservations into those parts of Mars with no economic benefit. Along the way you would have broken promises, broken treaties and maybe the odd slaughter of thousands of Martians more or less like the white settlers did to the American Indians. No doubt the spaceships to Mars would have all sorts of books and movies on how the west was won to educate Earthlings on how to go about settling on Mars. Sort of in flight training If you like. After-all the trip to Mars isn't going to a short trip and there will be plenty of time for reading.
All this of course is pure fantasy. No evidence of life forms has been proved. Just as well. H.G Wells scared the wits our of many radio listeners who tuned into a radio station that was telling his story "War of the Worlds" It now seems that mars is there for the taking. Prime real estate just waiting for the developer. Virgin country untouched by man. Great rolling plains of beautiful red rocks and red skies. Flood free as far as the eye can see. Unspoilt except for a bit of space junk sent there to establish prime places to settle.
The whole question of whether or not people should live on Mars comes down to money. Yes, money. Unless John Doe is a millionaire he is doomed to be an Earthling for life. No big Martian ranches for him. No living life enclosed in a dome waiting centuries for the politicians to approve Martian Terra forming and come up with a plan under budget and one that actually works. No, John Doe will be doomed to live on Earth without ever knowing the exhilaration of being cooped up in a dome with the prospect of imminent death should a meteorite crash through the dome.
I am of the belief that the huge cost of sending people to Mars will result in just a select few who will establish a base and then set out to find and colonise a planet similar to Earth in atmosphere capable of supporting life. Should people be allowed to live on Mars. Emphatically, yes. It is essential if mankind is to survive. The sun is just a star. Ask anyone who delves into astronomy what happens to a star eventually.