It can't be done. It would cost an enormous amount of resources to build a sustainable environment and send people to live on Mars (trillions of dollars).
Humans seek to survive, and there are people in Africa literally eating dirt. Once a human life is created it will do everything it can to survive. As resources are sparse, many people live in terrible conditions and compete to live. This competition irreversibly pollutes the environment. A common example is over hunting to make a quick buck, which leads to extinction of a species. Or a chemical company seeking to make profits, then dumping waste in a river. That is the way of life, and a high population causes conditions on Earth to become worse.
"For a few cents a day you can help an African child," people around the world are starving, and resources aren't spared to fix global hunger. If a few cents cannot be spared, then how can trillions be spent to just "send people to Mars"? The solution must occur on Earth
Since you directly asked me - the issue is agriculture. People in North Korea are starving because its difficult to grow food in mountains. People in Namibia are starving because it's difficult to grow food in the desert. But humans will do anything to survive, and will eat grass if they have to. I dont really think there is a solution for me, a normal citizen. I think if what I say is true, then some nation or force will ultimately take control over all people and actions. Technology is increasingly improving, and technological advancement gradually gives people more control over life. Drones, robots, AI... but I think all of this would occur well beyond my lifetime