Take the Survival of Humanity to an investor's meeting, or throw it into a business plan, and see what develops.

I'm not being glib. What are the potential business justifications for establishing a presence on Mars?

Permit me to try: could the results of science and exploration (perhaps including sample return) be of sufficient commercial value to make the costly endeavor worthwhile?

Or (more ambitious) maybe various governments, universities and companies could buy space on unmanned orbiters/landers for experiments they want to put above or on Mars.

Or how about this (longer term and wildly ambitious): half the nations of the world, it seems, want to go to Mars, but none of them want to spend the money required to do it. What if they could buy transportation and habitation for a fraction of what it'd cost to develop it themselves? Would there be any takers?