Who says everyone needs to contribute back? If someone wants to live off absolutely no money in a hole somewhere, why not let them? The idea is there will be a percent that will give back hand over fist more then those that want to live in a hole. It doesn't need to be a 1:1 ratio, it doesn't even need to be a 10:1 ratio. Some people simply do and are worth a hell of a lot more to society then that one guy who wants to live in a hole.
And if society shifts enough, it may actually start to make those people living in that hole feel bad, and they too will eventually crawl out and try to better society. There are a LOT of different ways of benefiting society, not just earning minimum wage working at Tbell. That is something that can't be quantified in economics. Empowering people and making people feel like they can make a difference without being punished for simply trying is extremely important. Our society IS way too dependent on the whole idea that you have to get ahead over everyone else, so you have the bloody battle of capitalism in which everyone tries to claw, scratch, and fight their way to the top... All so they can buy $250 plates at an expensive restaurant somewhere.
I'm actually in a slightly different category. I think a stipend for the average citizen is a great idea. I also think a income cap is also a very good idea. This most definitely will get a lot of hate, but income has huge diminishing returns for people. Perhaps not for a company as it can continue to grow, but once you meet a certain income to cover basic necessities as an individual it makes less and less of a difference. So if you have a income cap at like 100x the yearly income of a minimum wage worker, like $7.5 x 40hours/week x 52 = $15,600 you'd end up capped at a yearly income of $1,560,000, which is more then enough to live off of comfortably for like 95% of the population and that 5% that spend in extreme excess would simply have to trim back their ridiculous lifestyles.
If the person earns more then that amount they either have a choice of paying it in taxes (which then gets put into public services and bettering the country as a whole) or reinvesting it in wherever it came from, such as a company. And if that company has an excess income it'll look to either reinvest it, which helps society as a whole, or they'll simply sit on it, just like the person in the hole. But eventually, someday, they too will realize that just sitting on money doesn't do anyone any good and there is no reason to actually acquire money just to have money.
Obviously there are a lot of ways to cheat the system (such as having your company pay for everything as a business expense), but we have branches of the government to deal with that and I'm sure they'll get better at doing it once they have more practice.