You make good points. Like I said, I support a Mars colony under the right conditions. I say it's myopia to ignore a much better investment. All the benefits you name pale in comparison to the benefits (or loss savings) of paying down the debt. If we proceeded on a Mars colony now, the US would likely slip into a Greater Depression before we could reap a benefit large enough to prevent that. Due in part to those wars we're too close to the abyss. The best choice is to get away from the abyss before focusing attention elsewhere.