Mars can already be useful as a springboard for space exploration. It's a literal stepping stone, both closer to the belt and outer planets in terms of distance, but also in terms of delta-v, since both the gravity well on Mars is smaller, and it's higher up in the Sun's gravity well, too. Any future space exploration and exploitation will be made tremendously easier if you can launch from Mars instead of Earth.
Mars is, even at absolute best, a dump: dry, cold, airless, at the bottom of a gravity well, and subject to dust storms besides.
We can build much better outside of gravity wells. Whatever you would land on Mars is more useful in solar orbit, parked next to any convenient asteroid.
You can't do ISRU in orbit. I don't know of any resources available on the Moon that would allow you to do ISRU there either. Ceres might work, but the inclined orbit may make that impractical as a stop.
We do ISRU all day, every day right here, in the millions of tons.
"A stop" is not just useless, but is actively harmful in space transportation. You go, for free, until you get there, and then use up fuel stopping. Starting and stopping are exactly what costs. Stopping halfway makes the whole trip cost literally twice as much.
It's also 'for free' to continue from LEO to anywhere else, but it can still make sense to refuel in LEO rather than launch with all the fuel requirements you need for the mission from Earth surface. The delta v required from LEO to another body is lower than that from Earth surface there. Delta v required from lunar orbit to some non-terrestrial body is also lower than that from LEO, and it could potentially make sense to do refuelling from there in order to get the maximum possible delta v leaving Earth's gravity well. Finally, the delta v required to reach the belt and Jupiter from low Mars orbit is lower than that to reach them from Earth. That means bigger payloads can be sent to these destinations, or even potentially any payload at all; it is only barely possible to reach a Hohmann transfer to Jupiter from Earth with SpaceX's Starship's claimed delta-v, whereas from Mars there should be several km/s of extra delta-v to spare.
Refueling in LEO or high earth orbit is fundamentally different, in every single particular, from stopping somewhere halfway.
Until you understand this, everything you say about space travel will make zero sense, and furthermore will deeply embarrass you for long after you finally catch on. You make a fool of yourself by continuing in this vein.
You can do the calculations yourselves. Refueling in LEO is energetically more costly than a launch from the Earth surface to escape. You will end up using more fuel overall if you launch into LEO vs. if you take all the fuel you need from the Earth's surface in a single launch. If there is a difference, you haven't explained it.
No, you did not. You have made such false claims as 'If you can't get there without a stop at Mars, then you really, really can't get there with a stop at Mars.' This is a claim that is easily shown to be false by calculating the differences in delta v from Mars to belt/outer planet destinations vs from Earth. You then claimed what you meant was that it takes more energy - but so what? It takes more energy to refuel in LEO than it does to launch a ship from the Earth surface to escape. Basically this entire time you have simply just claimed 'no, you're wrong' without any calculation to back it up, and the few claims that you have made have been ludicrously wrong.
