TL:DR; Your oncologist friend does't understand science or that money doesn't buy solutions or guarantee a linear speedup of results.

There's always going to be problems and no matter what problem you're invested in, someone has a more dire problem that they think all the money and resources should be spent on.

And the thing your oncologist friend needs to realize is that throwing more money at a problem doesn't yield better results. We could spend every penny the Earth spends on space for the next 50 years and not get a solution any faster than the current level of research.

The other issue is this, what's so special about space? Cancer has been with us since forever. What if instead of investing in computers, we spent all that money on cancer research. What if instead of investing in electricity we had spent all that money on cancer research? What if instead of investing in exploring the world, we spent all that money on cancer research.

We could walk back through history and smack down every sort of human endeavor not directly related to cancer research and criticize it as a waste of time compared to any problem someone feels is more important and needs immediate attention. If we did that we'd still be in the stone age and that's not going to help solve serious problems.

Some of it is that it's not always apparent what benefits we'll gain in the long term from unrelated fields of research and discovery. What did electricity do for cancer research in 1882? Not a damn thing. But in 2018 it powers computers and labs worldwide that help us make huge advancements, cure people, increase life expectency. Who could have imagined that in 1882 though? But I am sure people lined up by the truckload to poo poo electricity as a waste of time when there's "real" problems to solve.

What did digital computers do for cancer research in the 1940's? Probably not a damn thing and it was decades before they were powerful enough, available enough, and cheap enough to become the backbone for research of all kinds. We've probably learned more and made more advancements in cancer research thanks to computers in the last 40 years than the last 40,000 years. Seems worthwhile to me.

We can't predict what avenues of research and exploration will lead us to the knowledge that changes the world. Yeah, it may not always be obvious and not everything happens on the immediate timescale that we would like or hope for. But it is shortsighted and hopelessly naive to say, "this will never have a benefit the problems I care about so we should abandon it, clearly it's a waste of time."

>It’s hard to argue with her. $400B/yr would fund a lot of research that would benefit humanity a lot better than a coordinated mission to Mars, even though it would be very exciting to see in my lifetime.

How about this: A manned mission to mars has serious hurdles relating to human survivability. The unprotected radiation exposure on the trip and on Mars would certainly have affects leading, among other things, higher cancer rates among astronauts. These are problems we're aware of and need to be solved. And what if that effort leads to serious breakthroughs in cancer research or prevention? And we know space travel has serious effects on the human body, if we study that and gain a better understanding of the human body as a result that would have a hard time not having benefits for cancer research, a subject largely centered around a problem with the function of the human body in certain cases.

There's all sorts of ways manned space travel can lead to benefits for all mankind.