Turns out the real overpopulation is in places people want to live.
I think most people don't realize how inherently unstable our society is, and how quickly civilization can devolve.
Nuclear war is a huge issue. We've had three conflicts this decade that could have led to a nuclear war. All of which are still unresolved.
I'm kicking myself for engaging with this at all, but that's poor reasoning if you're worried about nuclear war. The risk of MAD forces a detente, if there were a (perceived) hedge against it, that increases the likelihood of MAD happening.
If nuclear war happens, Mars colonies depend on expensive, technical supply chains on Earth that will be destroyed.
We take for granted a whole damn planet where water falls from the sky, food and fuel come out of the ground and there's abundant amount of replenishing atmospheric O2 available for ubiquitous reaction and combustion.
Without resupply from a nuked Earth, you're left with the fact that food, manufacturing, construction, etc all depend on, at the very least, atmospheric oxygen, and Mars will never hold a meaningful atmosphere. Without atmospheric oxygen, and thus combustion, when it comes to supply chains required for existing anywhere, you aren't building infrastructure, you aren't growing food without nutrient supplies, and you aren't manufacturing sustainably, efficiently, or at all.
And that ignores that Martian dust and soil is toxic[1] to life, which requires even more resources to mitigate, remove, keep out/off of people and living things, and even more resources to treat and maintain the soil if you ever want to use it to grow food.
Earth is the one shot people have, and a nuked Earth is infinitely more habitable than Mars. Even the bottom of the ocean is more habitable than Mars. It just does not make sense as a backup option to Earth. And if Mars is a pipe dream, life isn't leaving this solar system and surviving independently as anything resembling humans.
My rationale is, when SpaceX actually launches the first Mars mission, the price will go hyperbolic. It will be the stock pump of the century. I estimated what valuation it would hit (~$5 trillion at the time), then looked at the current valuation, realized this will 50x in the next two decades, and concluded it would make a great investment.
You have to pick one side, not both.