Things will grow outdoors, even if they’re not the things we want growing.
We already know where major deposits of natural resources are.
There’s an ionosphere, meaning the surface isn’t bathed in deadly radiation.
Parts of it, such as the poles, will likely remain habitable.
The big issue, though, is that transporting any substantial number people to Mars would require many trillions of dollars of investments in space transportation. It’s just not feasible to ship a large number of people to another planet. Even if we could start a colony on Mars, most of humanity will still be stuck on Earth and they won’t have much interest in supporting a colony on another planet if they’re being left to die.
Earth still has plenty of benefits:
The big issue, though, is that transporting any substantial number people to Mars would require many trillions of dollars of investments in space transportation. It’s just not feasible to ship a large number of people to another planet. Even if we could start a colony on Mars, most of humanity will still be stuck on Earth and they won’t have much interest in supporting a colony on another planet if they’re being left to die.