1. Humans can live in space for extended periods (eg the ISS);
2. We have the capability to land something on Mars and take off again, rendezvouzing with an orbiting spacecraft. We did this on the Moon;
3. We have the capability of getting enough fuel and payload into orbit and then sending that to Mars and back. Now this part is tricky because every pound of payload you need has a knock on effect in terms of more fuel needed plus more fuel to carry that fuel. This I think is actually the trickiest part but largely comes down to a function of launch costs.
That all being said, it looks like it'll cost hundreds of billions of dollars and be an active mission for ~2 years. Is it worth it? That's a reasonable question to ask given how many unmanned probes we could send for that same money and what the value is of sending a meat bag to another world.
Now colonization is a whole other beast. My definition of colonization is that the colony is self-sufficient. For this, IMHO we simply don't have the technology. Far from it. Too much of what we rely on is provided "free" by the Earth. Air, water, plants and animals. Resource extraction is ludicrously cheap compared to anything in space or on another world.
But think about the daily things you need: clothes, food, computers, shelter, transport. There's a complex web of dependencies on any one of these things such that a good portion of the world is needed and a pretty significant number of people are required.
Also, does Mars even make sense? It has almost zero atmosphere. I've read that Mercury may in fact make much more sense. For one it'll solve the energy problem (solar on Mercury, anyone?).
Not that living on Mercury is without problems of course.
Landing per se shouldn't be impossible. We landed people on the Moon a long time ago. Recent advances in magnetic shell aerocapture are really exciting and make landing on Mars more feasible. The real question is whether we can learn how to do it in an economic and sustainable way; unlike Apollo.
> It would be better to colonize the moon
I agree with this. Going straight for Mars seems unwise. We should expand slowly out into the Solar System, step by organic step. Even better than the Moon would be Low Earth Orbit. A colony in LEO would have same-day access to Earth in either direction, and would benefit from being inside Earth's magnetic field, which would allow the designers to cut the mass needed for shielding significantly. Big savings.
A LEO colony would be close enough to Earth that people on Earth could teleoperate robots in the colony in real time with minimal lag, allowing it to circumvent the bootstrap question of "Where do people live while it's being built?"
A LEO colony would also have to built using bulk physical resources from the Moon or the Near Earth Asteroids, building up our manufacturing base there, and serving as a "shore leave" destination for people working further up in Geosyncrhonous Orbit or elsewhere Cis-Lunar space.
Once we have a basic torus capable of holding, say, 10,000 people, it could serve as a staging area for venturing deeper into the Solar System, such as Mars. But personally even then, I wouldn't advocate for Mars. After all that work of moving humanity out of a deep gravity well, why climb into a new one? Space is where all the solar energy is, and all the resources of the asteroid belt and the moons are (gravitationally speaking) close at hand.
> It’s a massive waste of resources which could go towards making earth better, where we’re all stuck anyway.
Now here's where I disagree with you.
1. In no way did colonizing Australia or North America prevent England from improving the homeland. You can do both! Heck, Elon Musk is already doing both. The whole point of Tesla/Solar City is to move humanity off fossil fuels.
2. Space colonization can be part of the solution. Imagine industrial processes that have very polluting intermediate steps; they could be done on the Moon where you don't have water or air to worry about polluting. Earth could be cleaned up by exporting those industries to space. The Moon could also serve as a much better repository of high-level nuclear waste than Yucca Mountain.
And of course in the very long term, the Solar System has the energy and material resources to support a human population 10,000x bigger than Earth does. As much solar energy as Earth receives, space receives a lot more. As much iron and PGM and carbon and water as Earth has, space has more. Europa alone is estimated to have 2x as much water as Earth. And so those resources can support more people who have more ideas who solve the very problems you want solved.
A LEO colony would be a staging point for colonists and ships, but not a ship itself.
In colonial times for example it was common for a woman to go home to Europe to give birth. Will that really be feasible in mars or the moon?