Any of those leaves Earth thousands of times more habitable than Mars. They even leave Antarctica and the sea floor thousands of times more habitable than Mars.
What plants would resist the massive amounts of radiation, or perchlorate soil?
Note that we don't even know if any plants today would actually be able to fruit in the low gravity environment (nevermind if any animal would be able to successfully procreate).
You would generate a magnetic field at the center of the colony to deflect solar energetic particles and galactic cosmic rays. The colony would produce compost with biowaste and use that for soil. There are various ways to remove perchlorates from soil. One avenue of research is to find an optimal mix of martian soil and compost to allow plants to thrive.
The points you are making are excellent but I believe solvable. Also we do know if plants can fruit in space. We've already grown tomatoes in space and they are fruits of the tomato plant. And that was zero G.
You are going to run into energy generations REALLY fast trying to generate such a massive magnetic shield, Not to mention all the other massive energy needs for mining and processing material.
Also nobody has yet produced a self-sustained biodome.
I'm not really sure farming will work on Mars with sunlight alone given the distance from the Sun. Still, you have gravity and reasonable day length and even some atmospheres, not to mention a lot of mass available - that already makes a lot of things easier.
