The romance of exploration. Voyages of discovery, with intrepid heroes inspiring others to go with them or to pay their way . Columbus had Ferdinand and Isabella as his patrons. Lewis and Clark had Thomas Jefferson and, by way of his office, the people of America.
Perhaps it all peaks with the Apollo program landing humans on the Moon, in what can be described as a money is no limit program. A nearly pure expression of the Cold War. Let us also remember that Congress canceled funding for the last 3 missions.
There have been a lot of thoughtful folks who believe that the Apollo program was in the wrong sequence. They saw the correct progression as moving from the X-15 and the Air Force DynaSoar space planes to a full time presence in Low Earth Orbit and then to the Moon. The Air Force was well into developing a Manned Orbital Laboratory (MOL) but it did not make the cut versus Apollo. NASA did come up with Skylab, post Apollo. That probably should have come first, according to the LEO advocates.
NASA tried to apply the “Can Do” magic to the Shuttle. Given the original objectives of a flight every one or two weeks, it was a miserable failure. Blasphemy you say? Let me use an old fashioned business term we uttered when someone proposed spending money on anything new. How do I get my bait back? How does this pay for itself? Fully accounted for with all program spending included, each Shuttle flight came out at $1.5 Billion USD.
Did we benefit from the Apollo program? Did we benefit from the Shuttle program? Complex questions and answers. Where they worth it? IMHO, that is truly in the eye of the beholder. And the arguments get circular.
Sarcasm has it that we got the beverage Tang from Apollo and not much else. That would be wrong, both about Tang and the Apollo benefits for technology, education, program execution knowledge. I've linked in an older article about the subject that still rings true. The issue to argue about is could we have had the same benefits by building an big LEO space station first, thus making Moon explorations more affordable and sustainable?
Was Apollo worth it? I believe the answer is yes, and that is despite our country giving up technologies like the Saturn series rockets and the F-1 engine that powered the Saturn 5.
Regarding the Shuttle, many feel NASA got caught flat footed by the early end of the Apollo program, felt the lash of threatened budget constraints and dreamt the right dream. IMO, they just got the scale of the technical challenge and the breadth of what to try to field very wrong. Was it worth it? I think the answer is no. And, yes, I worked on the program. $1.5 BUSD per launch! We did keep the solid rocket booster technology and the main engines (SMEs). The expense of the program prevented too many other things NASA could have started, IMO.
So, why a manned mission to Mars?
If you have the time, I would invite you to read Andy Weir's book, “The Martian.” Also a good movie but the book more thoroughly explores the subject of astronauts on Mars. It is a work of fiction, so items like the threat of wind pushing things around is fiction. The Martian atmosphere is far to thin to tip over an ascent stage.
Our Mars exploration to date has been primarily focused on the search for life outside of our planet's environments. We have a sturdy robot travelling across the surface and multiple craft in orbit doing photography and science measurements. The next NASA rover is scheduled for launch next year and other countries are planning efforts. It is true that getting to Mars and landing or getting into orbit is notoriously hard.
It has been said that much of the past years of robot science activity on Mars could be done by an astronaut in a few hours. Perhaps true but the robot doesn’t care about radioactivity levels, micro or light gravity and other hazards involved in getting to Mars, staying there and getting back. The rovers, landers and orbiters require no life support or consumables, run no medical risks.
On the other hand, a human can fix things, troubleshoot, organize, plan and other tasks that our robots can not do. We have good examples from servicing missions to the Hubble telescope and some satellite rescues. We have good examples of fixes that could have been done with by an astronaut in a few minutes, had one been present.
One link below is to an intensive, very tech discussion on the hazards to humans on the surface of Mars and what should be done to accurately calculate the risks involved, perhaps even the viability of going there. It is most assuredly no “Roamin in the Gloamin!”. In particular, the radiation hazard is daunting, in both flight mode and on the planet surface. Many of the advanced discussions about long term stays on the surface include burying or covering any habitats and enclosed workspaces in Martian dirt (regolith). Even the rovers will have to be speedy to minimize exposure time. (Maybe a Tesla rover with a Ludicrous mode?)
My belief is that in discussing near term manned Mars missions, say by 2030, the U.S, Elon Musk, etc. are once again, like Apollo, trying to “hit a home run.” We can't even assure funding for the one space station we have and we are talking multi-billions for a moon gateway and a trip to Mars. I am truly not worried about the sun going nova in a billion years and not inclined to panic about a dinosaur killer. I believe we should consider ourselves and all of the nations of Earth decades away from an attempt, probably many decades. If we go, we need to get over our peer and near peer rivalries and go as a consortium.