(Hey so I apologize if this has been touched on in the main thread, but I didn't spot anything related so starting a new one).

We should consider even further: what about consequences of successfully colonizing Mars? I feel it would mean almost certain doom for both planets. I'll explain:

Imagine all of the hurdles mentioned in the linked blog are overcome. Improbable for the U.S. or EU, sure, but consider China. If everything goes well, they end up with a sustainable outpost with several hundred to several thousand inhabitants and a reliable supply line back to Earth. Everything is great, yeah?

But looking a bit further down the timeline, we will end up with generations of humans native to this outpost. All living deep underground, rarely seeing the surface. Sure there would be domes you could visit to check it out, but they'd probably see as much traffic as a planetarium or scenic vista - more apt for school trips than any part of daily life.

We know very little of the role of epigenetics in these conditions, but you might imagine that tunnel dwelling folk in weak gravity are probably going to express genes differently during development, than we see here on Earth. Different diets, different light exposure, different gravity and even different focal lengths will all have an impact. The forces of evolution will bear an increased impact here also - children that blossom into more Earth appropriate bodies will have increased pressure against their thriving in these conditions. Social forces will likely begin to exclude them from the gene pool, accelerating the occurrences of whatever Martian traits emerge.

These generations of inhabitants would eventually put pressure on the supply lines from Earth via the growing population. Or some enterprising politician will manipulate the supply lines in order to exercise despotic authority over them. Eventually the Martians will see pressure to become self sufficient. This will plainly lead to a revolution and independence - an intolerable insult the the patron government. Back on Earth, the strange look of the native Martians will stir racist hatreds and clamoring for subjugation with extreme prejudice. Recall that in the past few years we've seen extreme hatred rear up over the pettiest of differences, to the point where neo-nazis are flourishing and attempting coups in the most powerful nations. Hating weird gray/green skinned, 8 foot tall spider people from Outer Space would be reaaaal easy for these people.

The Earth will send their troops and bombers. The Martians will burrow deeper and humiliate those invading troops with relative ease. The Earth will maybe nuke the place? But that will have very little effect, even the aftermath of fallout and irradiated rock will be negligible to the Martians. But they will be angry. And it would take little effort to rig something up and launch Phobos at the Earth at 1% c.

But the Martians would soon learn that they were dependent on Earth for more than manufactured goods. Their delayed access to the internet would disappear, along with scientific advancements, intellectual culture, entertainment and archives going offline and leaving them with whatever had been cached/stored in their local cloud hardware. Would Mars have developed a chip fab (and the equally important thousands of suppliers for a chip fab) by this time? Medical knowledge? Would they have needed expertise in Computer Science? Imagine if some disaster left Earth with little more than a single hospital and a computer retailer, how would we recover?

Mars Colony may just soldier on for a while, but more than likely would ultimately succumb to genetic degradation, scientific stagnation, room to grow the civilization, lack of elements or molecules that are difficult to procure on Mars, etc.

Colonizing Mars is the worst idea. Just the worst.