1. Professor Stephen Hawking is probably right, we do need to get off this rock, sooner rather than later. "It is important for the human race to spread out into space for the survival of the species"
2. We evolved to survive on an unguided mudball, third rock out from a slightly variable star; we haven't found the thermostat yet. Sooner or later, our luck will run out, one natural extinction level event and it's game over.
3. It's worth boldly going somewhere that will probably kill you, if and only if, there is a damn good reason to be bold.
4. Our current space drive technology consists of throwing stuff as hard as we can in one direction so we get a bit of usable thrust in another. It's a losing game, a pathetically inadequate method, compared to our needs and dreams.
5. Mars has a deep gravity well, with an unbreathable, and (worse) unflyable atmosphere. We have no known scientific or commercial reason to go there, or means of survival if we did.
6. Robots are expendable, cheap to make, specialized, and inexpensive to remotely control, even in space. Humans, are expendable, cheap to make, generally useful, but ridiculously expensive to operate, especially in space.
7. Robot probes in space, historically have produced vastly more science per dollar expended, than humans. We should boldly go somewhere when we intend to colonize, not to send back wish you were here postcards...
8. To colonize, there must exist usable resources, in vast and accessible quantities, easy pickings. At minimum we will need Carbon, Hydrogen, Oxygen, Nitrogen (CHON), plus metals, trace elements and usable energy. There must be shielding from radiation and the other obvious space hazards. Such resources do in fact exist in limitless abundance, in open space, as the larger comets and asteroids. The orbital vectors and masses (that we know about) are currently a little inconvenient.
a. We (Humans) need to invest heavily in science and engineering that may lead to much better space propulsion, techniques for mining and commercial and civic use of such open space accessible resources.
b. We need to develop much better remote probe and manipulation technology, so the robots can investigate anywhere we want, and possibly alter the orbits of low mass, high value objects, as cheaply as possible.
c. We need to develop space habitats, on comets and asteroids, to exploit their resources as a long term (effectively infinite) space habitat.
d. Our most likely cause of extinction as a species is our non-existent space colonization strategy. We are led by a clueless collection of dumbass politicians who cannot see beyond Buck Rogers pointy spaceship sci-fi and (much more importantly) their own short term military and pork barrel political aims. There is no coherent, international, long term, human survival and colonization oriented strategy.
e. When some damn big rock arrives at 5 miles per second, we are all going to look equally stupid and just as extinct; fossilized human politicians will look almost identical, as the "intelligent" humans remains.