Mars is just a placeholder for an alternate home to earth.

Most technologies developed for these missions will be reused or new ones will built on top of them.

Yes, I understand Mars is a placeholder. But I life in a new planet that must be terraformed is even worse and more hostile to human life than, say, colonizing a new continent. Or building undersea colonies, like someone else said. Even the colonization of an Earth-like planet would be almost impossible, and we aren't aware of any nearby.

We would be going to a less inhabitable place, while taking all the problems of mankind with us. I must echo the grandparent post: Earth is not the problem -- we are.