By the way, I'm a big SpaceX fan and I hope there will be an outpost on Mars, but a self-sustaining city is just unrealistic, sadly.
If it's ever going to happen we need to move forward. Going to the moon was great but we've stalled since then.
We talk about jobs ending. We'll space research and development is a fertile ground for new jobs.
People who don't agree with you about it being a worse place to live than Earth in almost every regard might want to live there. I don't think Mars is a "worse" place to live than Earth in general, though it's certainly more challenging to live there. On Earth, humans have lived everywhere it's possible to live, not just where it was easy.
Antarctica was uninhabited until comparatively recently not because it isn't a nice place to live, but because without modern technology it's basically impossible to live there. The Sahara has been inhabited for thousands of years.
The Andes and Tibet are places which are so hard for humans to live in that the populations there have genetic adaptations to help them survive the low-oxygen environment. I mention that not to suggest that Martians might evolve the ability to breathe Martian are, but that humans haven't allowed mere inhospitability to stop them living in a place: history tells us that if it's possible to live somewhere, people will live there.
Depends which parts of Sahara, some are certainly livable.
Mars is a lifeless desert and you'd be mostly stuck inside anyway to avoid radiation. But maybe the goal of building a self-sustaining colony would give the people a clear purpose that would offset the discomfort.
The OST prohibits a signatory to the treaty from claiming any celestial body. In practical terms, a base on Mars would, unless it was exclusively built with components launched from the same country, be a patchwork of jurisdictions. This is in fact the situation with the ISS, which is (probably) the only place in the Universe where the territories of USA, Canada, Japan, Russia and Europe are only seconds apart.
Of course there is always the possibility of a New Boston Tea Party. International convention is that a seceding state isn't bound by the treaties of the original state, so if a Martian government were recognized by Earth's governments they could try to claim Mars.
The more practical concern is what it would mean for SpaceX to "claim Mars". I could claim Mars right now, but it wouldn't benefit me at all unless my claim was respected by other states. If the US, or anyone else, could steamroll in and take control of a SpaceX-founded colony that was purporting to be independent, then the claim would be worthless.
And no, you don't get to claim the entire planet by planting the first colony.
A trip to Mars is a stretch goal that we need to start as a species. We know that our lifetime as a species is limited on earth so the sooner we start figuring out how to get off the planet the better. Yes, we might fail but then we'll have to try again and again.
Musk has made himself the spokesman for that task. No one else seems to want the job. Yes, he's a dreamer and might be overselling the task but that's what we need. We need to start. I can tell you that if we never try it will never happen.
My hope is that he becomes so rich that he owns all of Mar's resources. Yes, he'll own them for a bit but it means mankind has made a large step forward. Go Musk!