Earlier quoted context omitted.
I think the simple answer is 'hedging'. Cancer, hunger and the like are unlikely to kill the entire human race in one go. A climate event or asteroid could, which would render all other efforts redundant. Mars exploration means hedging the survival of our species. A diverse portfolio is where the smart money is.
This is a nobel reason, however I imagine the real answer is closer to sex appeal and money. Also, who should determine how the resources of humanity are deployed? People who arbitrarily have gained control of the resources? For a tiny fraction of what is spent on space, we could solve world hunger and water. It also seems a well fed and hydrated global population would be much happier, healthier, creative and produc…
No we realistically can't. How exactly do you propose doing that? Keep in mind that there is a ton of precedents where local governments withheld foreign aid (which was supposed to "solve hunger" at least at that part of the world) to enrich themselves and/or to control their citizens. How do you solve that with any amount of money? Bomb the "bad governments" into submission? Just keep the money in some account waiting for those governments to become more civilized? Might as well colonize Mars in the meantime