The soil can be cleaned or brought from Earth. Do you really think that life on Earth in the next 10-20 years will be better and safer than on Mars?
Oh my. The energy required to transport soil from earth to mars alone would be staggering. The environmental consequences on earth from the CO2, methane, NOx, SOx, CO, aluminum sols, the perchlorate from solid rocket boosters, and a myriad of other pollutants that would result boggle the mind.
Life on earth will continue. The standard of living for humans will not precisely because of our own shortsightedness and ignorance. Many, probably most species extant on earth today will perish, not in the next 10-20 years, but before this new era (the anthropoceme) runs its flash in the pan course. Mankind might well be among those that doesn't ultimately survive. But along with cockroaches and rodents, man is extremely adaptable, so I wouldn't be sure about that.
Life on earth is in large measure the result of the ongoing process of episodic mega-catastrophes leading to severe extinction events, combined with the constant roiling of the earth through tectonics, volcanism, and other factors. If we did not have a giant moon, a sister planet really, in near orbit, and a solar system littered with the debris of huge planetary body collisions raining down on the earth, life would not have reached the state it has.
This human caused catastrophe, climate disruption, is terrible for mankind and for the vast majority of species on the earth today. But that is just today. Wiping the slate and starting over fuels evolution of newer stronger better species to come. But that doesn't make it good for mankind or any of the species that do not survive the transition. And in the end it may not be good for life in general.
We have about 750 million years for intelligent life to escape earth and colonize other worlds. After that, heating from the sun will quickly extinguish all life on earth over the next half billion years after that.
For now, we have already severely fouled the land, air and water over the whole of the earth. What makes you think for even one instant that we wouldn't apply the same principles on mars, fouling it even further.
Technophilia, the love of technology, is truly a disturbing thing to watch in action. The blinders that people put on to get what they want (or think they want) regardless of, and utterly without regard to, the consequences is astounding.
Our greatest challenge is for mankind to wake up, grow up, and recognize how fragile and how precious our world is. The astronauts, cosmonauts and tychonauts who went into space all got that lesson. The astronauts who left earth orbit for the moon got that most intensely. We live on a small delicate world. It is a precious gift. And we are choosing through our willful ignorance, our arrogance, and our foolishness to destroy our home.