One thing I see missing from these discussions is the notion of diminishing returns. In the end money is an abstraction over the productive capabilities of our economy. If I were to spend twice as much money on food I could get twice as much. But if the world doubled it's expenditures on food I doubt food production would go up by more than 30% or so. If you read charity evaluations at Givewell they always ask "How efficiently are they spending their money" but they also ask "Could they efficiently spend more money if it was given to them."
Another is that it seems odd how selectively we apply this argument. I often hear about the need to stop space exploration until everybody is fed but I don't think I've ever heard someone say we should stop making movies until we end hunger.
Your observation about diminishing returns is an excellent one, but your comparison about space exploration and movie making doesn't make much sense.
The reason these people don't argue that we shouldn't stop making movies until we end world hunger is that (well, most of the time), the making of movies is not funded by the government, but by the private market.
It's a one thing to to argue that we shouldn't do Y at all as a species until we accomplish X ("we shouldn't make movies when people are starving"). It's very different to argue that maybe the government should completely prioritize X over Y for the purposes of allocating tax money ("let's not spend money on space until we can feed everyone").
It should be remembered that movie productions are subject to an impressive array of subsidies and movie companies the beneficiary of a great deal of government policy and enforcement.
That aside, there will always be a better cause to which all resources should be devoted. And usually problems which would result from a solution. Would a more rapidly growing world in which everyone has food but in which nobody has a job be a better one?
Or building interstates or sports stadiums or paying inflated union benefits and salaries, or military spending, etc.
The problem is the above are all politicized and directly financially benefit some voters, thus have cheerleaders and other irrational actors holding up this spending and defending obvious corruption and abuses. Science, when done right, is non-politicized and doesn't financially enrich voters directly, so there's very little "I got mine" mentality here like there is with other programs. Many of which turn into "make work" programs (bridges to nowhere, etc), if not outright entitlements (welfare).
Not to mention the philosophical and practical problems with welfare in general. Once you establish a system where being poor is favorable to not being poor, then who will pay for all these resources. As a Chicagoan, CHA housing is a lot better than what you can rent on your own unless you make a decent wage. My wife and I used to wake up every morning in the winter and shovel snow only to watch the CHA housing across the street have city employees do this for them. Hell, if the government is going to house you, feed you, shovel your snow, etc what incentive do you have to ever leave that system? None as far as I can see. Now we have an idle class of people involved in drug abuse and gang related crime and shootings, as well as epidemic of unwanted children used to further game the system for benefits. Give up on space exploration for the sake of the insatiable welfare state which inevitably creates massive ghettos, massive taxation, angry youth mobs, and religious radicalization? No thanks. We've watched this path unfold in Europe and want none of it.
Reducing world hunger isn't just about growing more food. It also involves working towards more harmony between and within nations - which requires money, time, and effort. There's certainly a diminish returns factor there - regardless of resources used, people aren't going to be all chummy tomorrow. But it's also a false equation to pit space money versus food money (in the US), as you'd have an easier time trimming fat out of the military budget.
Another is that it seems odd how selectively we apply this argument. I often hear about the need to stop space exploration until everybody is fed but I don't think I've ever heard someone say we should stop making movies until we end hunger.