But those people will always be a net negative for society, basic income or not. Empowering those who would make a positive difference if they had enough time/money sounds like a good idea to me.
I think those who are against a basic wage feel the current net negative portion of society would be a greater net negative because not only would they be receiving a wage, but they'd spend it on crap and society would still have to take care of them (hospital bills, food, etc).