Lately, we’ve had a lot of puddlefish whining about how “we” shouldn’t go to Mars. Some of them actually think they get a vote, based on economic illiteracy and the delusion that SpaceX is somehow part of the US federal government. [Closed caption for the hard-of-thinking: it isn’t.]
But others just think they are giving good investment advice... SpaceX investors can do what they want, but Mars is a frozen wasteland full of nothing but near-vacuum and rocks.
Elon Musk likes to answer this question by pointing out that it’s not a good idea to store all humanity's eggs in one basket. He’s right, but this kind of argument isn’t comprehensible to everyone, nor is it the full picture.
The invention of manufacturing, and the transition from an agricultural to a manufacturing economy, is called the “Industrial Revolution” because its effect on the state of not only the economy, but daily life and the entire human world, was... revolutionary. Unprecedented. Unimaginable. Understandable only in hindsight. Everything changed. Imagine trying to describe the modern world to your preindustrial ancestors.
“We took that black stuff that seeps out of the ground, set it on fire, and used the fire to turn things that do the work of skilled craftsmen, only thousands of times faster, and now we all have horseless carriages and talking abacuses that can send a message to the other side of the planet in the time it takes to cough.”