You’d have to ask the thousands of people for their own reasons. There are good answers from such people here. I can see it seeming appealing to some people as a great adventure and worth the investment/self-sacrifice.
@WMflight I think Mars exploration is a worthy thing to do, for research and science purposes. There are many other things people spend time/resources on which I would shut down before I would halt space research. We could easily provide for human needs without scrapping the space program. We need to stop thinking in economic fallacies and reinvent our banking, politics, industry, agriculture, land use and corporations to be intelligent, wise, ecologically sustainable, and humanitarian. Thinking of scrapping space programs “so money can be spent on better things” seems like a hugely out-of-proportion notion coming from flawed economic fallacies, to me.
As for notions of the need to colonize, let’s get some perspective on time scale and threats:
Mousterian stone tool Neanderthal culture: ~300,000 years ago
Anatomically modern humans: ~200,000 years ago
Behaviorally modern humans: ~50,000 years ago
Agriculture begins: ~10,000 years ago
Nation-states begin: ~6,000 years ago
Empires begin: ~3,000 years ago
Industry begins: ~300 years ago
Spaceflight and nuclear weapons: ~50 years ago
Man on moon, Soviet 20-second lander on Mars: ~45 years ago
Viking 1 & 2 landers on Mars: ~40 years ago
Curiosity Rover lands on Mars: ~3 years ago
Time until it may become obvious even to fools that we are screwed due to human-made climate change: 50–100 years.
Time until our sun runs out of hydrogen: 5,400,000,000 years from now.
@ETpro I don’t think the sun running out of hydrogen is our most pressing problem.
@Nullo Tunnel colonization? There’s “room” under the surface of Mars? So I assume you are thinking about using the tunnel room on Earth first, and on the Moon?
@mattbrowne Because it’s there and at some point can be done? Hopefully we outgrow that being reason enough to do anything. Some things are bad ideas.