gehenna:
To be fair to the concept, and putting individuals like Elon aside (he didn't invent the concept, after all), it's not about tourism. At least not for the first decades or century. And if it is about billionaire tourism, I don't mind the idea that a bunch of billionaires are off world for a few years at a time.
Just as we learned a lot in the 60s when developing for the Moon, and afterwards when evolving that development from learnings on the Moon, real problems on Earth can be positively impacted from what we learn by progressing space science. There is value in the effort.
That's why I wrote tourism. I hardly believe that tourists gain groundbreaking knowledge during a Mars flight that could be of greater benefit to mankind. That would be like expecting my passengers to perfect i.e. hydrogen propulsion for the next generation of aeroplanes. 😉