I think one of the things that a national income could very conceivably do is increase (not decrease) wages for lots of folks. Think about the protesting fast food workers. Now imagine that they all got $15k/year national income (roughly the equivalent of $7.50/hr). On the one hand, it may seem like they would be fairly happy with only $5/hr for working, but that isn't quite right. We have placed a value on non-working life of $7.50/hr, and have given those people the opportunity to reject working for wages that are insufficient. Many people, could now afford to look into better opportunities, including going into business for themselves. The pool of individuals willing to work for the current $8/hr mentioned may actually go down, while the number of customers, and the need to fill slots goes up. This would mean that McDonald's would need to pay higher salaries in order to fill enough spaces to deal with their business.