Space colonization would be an difficult, expensive, and resource-intensive proposition. For some, though, it is of paramount importance; it's easy to find examples of folks claiming that almost any sacrifice is worthwhile if we can "get off this rock" or "become a multi-planetary species." Environmental protections? They just pointlessly impede Progress. What if a dinosaur-killer asteroid shows up? What about the fact that solar changes will make Earth uninhabitable in many millions of years? Don't those outweigh the lives of a few birds or sea turtles?
Nah.
Even in a world on the brink of human-induced ecological collapse, Earth is a vibrant, living, durable place. Everything around us, even in many of the most hostile places, is alive. Much of the world is so friendly to life that preventing plants from springing up from the soil requires active effort. The number of animal species is in the millions, despite the destructive shadow of the Holocene extinction.
Mars, by contrast, is dead. No solid evidence of extant life has ever been discovered there. The soil is toxic. Radiation levels are far higher than on Earth. The atmosphere is a thin wisp, primarily of carbon dioxide. Water is scarcer than anywhere on Earth, and severe dust storms frequently sweep across the planet. It is a remarkably inhospitable place, and solutions to these problems are generally unappetizing options like "live underground in dormant lava tubes." These are only the conditions on Mars itself - the conditions in transit from Earth are likely to be worse.
The whole idea here - that humanity, facing vague but ominous existential risks, should seek to diversify by going elsewhere in the Solar System - is dubious. The largest risks to humanity's future don't come from science-fiction threats like giant asteroids or paperclip maximizers. They come from overconsumption leading to the collapse of the idyllic home that is all we have ever known, and that is a preventable problem - but not one that can be solved by living in lava tubes on an actual rock. No amount of quasi-religious talk of a stellar manifest destiny will change that. Our inheritance is a share of a magnificent garden, capable of providing for everything we need - if only we tend it properly.
That's something worth fighting for. Talk of running away to a dead and hostile world is a distraction, not a solution.