Not must be. Is probably achievable, and is worth attempting, even at the cost of lives.

You can argue from either the perspective of futility of attempt (no chance of success) or futility of outcome (success wouldn't be worth it), but I'm pretty convinced both would be weak arguments, both logically and historically.

I'm probably an optimist on Mars travel. I think, with a fuck ton of starships, you could get people living on Mars. But there's some big asterisks on that. You'd more or less have to live in the starships, dependent on shipments from earth, with self sufficiency failing on pretty much every category. Over a very long period, most people would probably die a bit earlier from radiation and dust. Not much would be produced of value. It would cost hundreds of billions of dollars, at least. And interest in it would rapidly decline.

The suspicion I have about self sufficiency pessimism is that it's an apples to oranges comparison. Are there any modern analogies? As near as I can tell, it hasn't been required after the 16th century, due to access to relatively timely transportation.

And if it hasn't been required, then how are we to look at existing practice and say we're bad at or incapable of it?

Comparison to what? We don't need an analogy. This is a novel environment and it can be evaluated on its own.

Self sufficiency failing on Mars vs what kind of self sufficiency we can manage now (while living on Earth and no needing to prioritize it)

Sounds like the early days of Australia. Maybe build a new Botany Bay? (Only half joking.)

There is no survival advantage to us on Mars. What are we all arguing about? This site is staring to feel a bit unhinged when it comes colonizing the solar system. Like SGC Ori unhinged.