As to it taking less fuel to get to mars then the moon... How? Just explain how that is possible.
Aerobraking. The vast majority of your spacecraft's fuel and cost is spent getting out of Earth's gravity well. If you've burnt enough fuel to get into a lunar transfer orbit, it takes just a little bit more to escape Earth entirely and go to Mars. But to *land* on the Moon, you need to spend more fuel to slow down and stop on the surface. To land on Mars, you just need a heat shield, because Mars has an atmosphere you can use to slow down.
So that's reason #1 why Mars's atmosphere isn't a joke.
I'm quite certain you could "throw" things from the moon to the earth. So the return trip wouldn't even take fuel. You could literally just give it a push.
Unless you can throw things at 2.4 kilometers per second, no. The Moon's gravity is less than the Earth's, but it's still serious business. You need quite a bit of fuel to take off from the Moon. You need fuel to take off from Mars too, but Mars's atmosphere has carbon dioxide: bring a little hydrogen with you (or use the local water) and a source of energy (solar panels or a reactor) and you can synthesize methane and oxygen fuel while you're there. No need to carry fuel for the trip home!
Reason #2 why Mars's atmosphere isn't a joke.
[Mars's atmosphere] is not enough to appreciably reduce radiation to the surface.
Oh, but it is. Mars's atmosphere is thick enough to shield radiation about as well as several inches of concrete, reducing radiation exposure by a factor of 2-3. It's also further from the Sun than the Moon, which reduces solar radiation by a factor of 2. Neither of these effects are enough on their own: you're right that Mars habitats will have to be underground too. But going outside is noticeably safer.
Reason #3 why Mars's atmosphere isn't a joke.
Mars's atmosphere doesn't provide complete radiation shielding, but it does provide complete protection from meteorites up to about 1-2 meters in diameter.
Reason #4 why Mars's atmosphere isn't a joke.
And finally, the Moon has craters and lava flows and that's all. Mars has those, plus volcanoes and canyons and ice caps and wind and clouds and storms and snow and glaciers and sand dunes and landslides and groundwater and river valleys and maybe an ancient ocean and maybe, once upon a time, life. Why? Because Mars has an atmosphere.
Reason #5 -- the most important one -- why Mars's atmosphere isn't a joke.
As to why not do it on earth? That question doesn't even make sense.
It was a rhetorical point, not a serious proposal. I'm saying that if you're going to spend your whole life hiding in a sterile burrow, does it really matter that you're on another planet?
For the record, none of these ideas are my own. I'm quoting chapter and verse from "The Case for Mars" by Robert Zubrin. Zubrin's got his problems -- he's a little too casual about the radiation dangers, for instance -- but IMO it's a good starting point for any serious discussion of colonizing the solar system.