The difference between you and I is that I don't know if it will work. You seem convinced there's no point in even trying. You're like somebody saying a ship will fall off the edge of the world if they sail off beyond the horizon. I'm saying, let's go find out.
Virgin is a for-profit company concerned very much with image. Their business model is entirely based around getting people back to Earth again safely. They're inherently risk-averse, because their passengers are paying to get home again.
NASA and other world space agencies lack the political support to do much of anything at all, and they are even more risk-averse than a company is, because what little support they do get is the result of a fickle public that's terrified of dead astronauts.
It seems to me, Mars One is a different beast entirely. It's a one way trip, and they seem very up front about the risk. I'm sure all 1058 volunteers in the second round are keenly aware they may die at any stage in this experiment, and have accepted that risk. It's a privately-funded, non-profit entity that doesn't need to worry about public approval, just public interest.
As for figuring it all out, we've known how to get to Mars for decades now. We've made great strides in landing technology, and awareness of radiation exposure with the latest Mars rover, among other missions. Their efforts to build the habitation structures on Mars will happen before they ever launch a live colonist, so if they can't do it, nobody will even be put at risk. Regardless of outcome, we'll have learned a great deal, found out where our limits are, and maybe pushed them a bit further.
Frankly I'm fed up with the complacency of this species, at everyone's willingness to just stay put on our fragile little world, and never try anything hard or dangerous. At least these guys are trying. Maybe they're naive, maybe they've under-budgeted and this will cost a lot more than they think, maybe things will go wrong, maybe some brave explorers will die. At least they'll have found where our limits are, instead of just guessing and naysaying when somebody thinks they can do better than those who came before.