It is very tempting to believe that natural resources in the space environment can be used to help support additional space exploration. Of course, schemes like this should be investigated, and developed wherever we can, but we should also keep in mind that we have no guarantees any of them will be practical, even if they are scientifically possible.

I hate to be the guy always pissing on the parade here, but this is a space forum, and critically examining these technologies is essential to evaluating, and eventually exploiting, these resources--or deciding not to.

In this case, we are depending on breaking the strong chemical bonds that hold the CO2 molecule together, and that requires energy, lots of it. This can be done, algae mastered the tech billions of years ago by harnessing sunlight to break carbon away from oxygen. But how will we do it? It will require collecting solar energy on a vast scale, or bringing in a nuclear power plant. Both methods will require importing a lot of hardware, plus all the infrastructure (there's that ugly word again!) to support it, not to mention a lot of men to install, operate and maintain it. That's a lot of mass that has to be lifted out of Earth's gravity well and then gingerly lowered onto Mars's.

The exact same problems will be apparent if we try to make H2 fuel and O2 oxidizer from local supplies of water by electrolysis, not to mention we'll have to go prospecting for all that H20, and then we'll have to mine it, or drill and pump it up from underground reservoirs. Again, not physically impossible, but it will require a lot of energy, effort, money and boots on the ground to do the job, no to mention the survey and exploration work that needs to be done just to make sure that those resources are there in a location, quantity and form we can recover.

All this will have to be done remotely for years just to get the operation started, long before the first bit of scientific or colonization activity takes place. I suppose that if we ever decide we want a permanent presence on these distant worlds, we're going to have to develop these capabilities.
But even so, our base will never be self-sufficient. Any local resources we can mobilize will only lighten the load we're going to have to haul there. We'll still need to bring everything else we need.

Right now, we can visit every spot on Earth and we can stay any place we want. Whether it be the tops of the mountains, the bottom of the sea, the deserts, jungles or the polar icecaps. But everywhere we go, we have to build a harbor or an airstrip or a road to bring in all the stuff we need to stay alive. Even Antarctica has water, air, and fish in the surrounding sea, not to mention coal and Uranium under the ice, but we still need to supply our bases there with massive logistics. And those other wastes we've explored we've never bothered to settle, even though we could if we really wanted to.

Space will be the same, only more so.