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I'm going to point you to Scott's basic income FAQ. It addresses your concern, and likely many others you may not even realize you have, far better than I can.

http://www.scottsantens.com/basic-income-faq

Specifically, I think this entry may be a good place to start:

http://www.scottsantens.com/wouldn-t-a-basic-income-just-be-stealing-from-those-who-earned-their-money