On the face of it, Ridley Scott’s film is a straightforwardly inspiring story of one man’s battle against the odds to survive until a gargantuan rescue effort can save him. A tale of a rescue effort that only works because a rag-tag bunch of renegades break the rules and fight the system to save their friend.

If all those phrases sounds familiar to you, it’s because they are. The Martian is just castaway in space: a NASA astronaut played by Matt Damon must use his wits to stay alive after a Mars mission goes wrong and he’s accidentally abandoned. Help does arrive when NASA, with the eyes of the world on them, eventually decides to spare no expense launching not one, but two, new rockets and diverting an existing space mission in a ludicrously risky attempt to rescue their guy. I don’t think I’m surprisingly anyone when I say it works and they do save him: this isn’t Game of Thrones – protagonists don’t die on the big screen.

That said, though it’s a familiar tale, it’s actually very good. The film was gripping despite its 2 and 1/2 hour length and predictable ending. It’s also hard not to get excited at the prospect of humans living in space; there’s a really good Lord of the Rings joke at Sean Bean’s expense too.

And, on the face of it, the morality of the tale is very simple too: if you can save the guy, do. However, this makes a big mistake. The Martian is a terrible example of how to save a life.

The key point here is cost. Just think of the enormous amount of money required to launch two space missions to save one person. It’s in the hundreds of millions, if not billions, of pounds. I’d try to put a number a number on it, but 1. that’s a lot of numbers and  I’ve only got 10 fingers to count on and 2. looking up facts is hard work. But I don’t think we need to put a precise number on it because it’s obviously massive.

In contrast, think of how many lives that same amount of money could have saved if it was used on, well, anything else worthwhile. Reducing poverty in the developing world, say. Or distributing malaria-resistant bed nets. Or sending aid to Syria. Even paying for more drugs, doctors and nurses for the NHS.

Now, you’ve probably got a few obvious objections to this. One, it seems pretty heartless: you can’t just leave a man behind, am I right? Two, why can’t we do both: reduce poverty and help Matt Damon? Third, the comparison is irrelevant as that money was never going to be spent to save lives: NASA would have spent it on something else.

I’ll come to those, but first I think we have to grant that, if we strip everything else away and just look at using money to save lives, saving imaginary Matt Damon’s imaginary life is a huge waste of imaginary money. If you were going to spend that money to save lives, you ain’t getting much bang for your buck.

Now back to the objections. The first is that you have to do something. The guy’s been left behind and you can’t just let him die. The problem with this is that there are lots of people in the world who we in the West, and our Governments, could prevent from dying by our efforts and with our resources. Sometimes we can’t put a name or face to them, but other times we can: we can single out individuals who, if they didn’t receive some healthcare they couldn’t afford, would otherwise die. This happens all over the developing world. It happens here too: the NHS has a limit on how much it’s prepared to spend to keep people in good health. We should help people, obviously, but without endless resources helping some means not helping others. All things being equal, saving lots of lives seems better than saving one. So Matt Damon must die.

This brings me to the second objection: can’t we help Matt Damon and do these other worthy things? Well, I don’t know about you, but once I’ve spent all my money on hookers and blow, I can’t spend it again. I mean, I could try, but I’m fairly sure my bank manager won’t let me. This applies to governments too. Governments may have a lot of money, but it’s not infinite and it always comes from someone: governments only get money by forcing people to pay tax. If you’d like to raise taxes so we can afford to save stranded Martians and do everything else, that means you’re paying for it. So, how much are you prepared to pay to keep Matt Damon alive?

The third, obvious response to this is to suggest this line of argument is irrelevant as NASA are assigned money for space-based shenanigans and weren’t going to spend it on anything else. This is obviously true, but hits a key point: when there are people dying of poverty and preventable diseases here, how can we justify space exploration? Don’t get me wrong, I think space exploration is super cool, and certainly more exciting than funding the distribution of malaria bed nets. I just don’t see how it’s justified in a world with obvious and preventable suffering.

As an alternative plot twist, how about the following? Matt Damon, whilst stranded on Mars works out how much his rescue mission will cost. In a moment of enlightened self-sacrifice he realises that thousands of lives on Earth could be saved for the cost of his rescue mission. He concludes his life is not worth more than that of thousands of people. So he stoically refuses to be rescued and instead convinces NASA HQ that, if they really want to save lives, they should abandon him, return the money to the US Government and insist it spends it on aid for the developing world. The rest of the movie follows the gripping tale of how aid get distributed in Sub-Saharan Africa.

You wouldn’t go see that movie? Okay, fine. I’ll admit the story’s not obviously as watchable. But I think the morality is much better. It’s what a morally perfect Matt Damon would do.

The point I really want to make isn’t that they should have left Matt Damon to die, or that he should have sacrificed himself. I suppose, if you are going to spend all that money on space stuff and won’t spent it on anything else, you might as well try and save him.

Instead, it’s a more general reflection that there should never have been an ludicrously expensive space programme in the first place, not when there are better things to spend money on, things that would do more good.