Products manufactured in space have zero carbon footprint. Indeed, they contribute no pollution whatsoever to the Earth's atmosphere or hydrosphere. This includes energy, since asteroid resources can be used to build solar power satellites which can beam low-cost, zero-pollution energy wherever it's needed.
In the far-distant future, it is likely that humanity will expand throughout the solar system, and the resources of asteroids are a key enabler. Experts have estimated that asteroids contain sufficient resouces to support a population a million times greater than the Earth.
But expanding into the cosmos is not simply a matter of needing the space and having the resources, rather it's a matter of necessity. If humanity does not expand into other planets and/or space settlements, we will become as extinct as the dinosaurs. Some calamity, whether global warming, or nuclear war, or bio-terrorism, or even an asteroid strike, will take us out. And like mammals followed the dinosaurs, something will rise out of the ashes and follow us. Earth is the cradle of humanity - but we can't stay in the cradle forever.
The only natural disaster that civilization can prevent is asteroid impact. By developing the technologies needed to deflect asteroids, we can prevent such a catastrophe. While asteroids as large as the dinosaur killer are only thought to impact the Earth once every hundred million years or so, there are millions of smaller ones which might strike once every hundred or every thousand years on average, causing billions - even trillions - in damage, while killing millions of people. We know of one such asteroid that has a small chance of impacting the Earth in 2036, and it is large enough to devistate an area the size of the State of Connecticut. While it won't have a global impact, it would still be a disaster beyond anything in the history of civilization. We can - and must - prevent such a disaster.
Think of this: if the dinosaurs had a space program, they'd still be here.
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