Mars is habitable by humans - barely. Future Martians will need protection from radiation, extreme temperatures and scouring dust storms. Their machines will squeeze water and oxygen from the environment. The children will develop delicate bodies in the low gravity. Finally, they will have to grow food on land that has never seen crops. On the face of it, settling Mars does not seem worth it.
Opposing these obstacles is the irrepressible force that led man out of Africa and around the world. There is something in our DNA that needs to move on to the next place, to colonize new lands, to spread ourselves into every available place. Some will stay back, like ancient Siberians convinced that the land bridge to North America only led to danger and difficulty. For these people, Mars is just another point of light in a sky that they rarely turn their eyes to see. They will leave it to others to reach out into space and grab the rewards of adventure.
Man will go to Mars and create colonies that will spread out over the planet until the crowds drive a future generation of explorers to the rest of the solar system and on to the stars.