I think the only argument against basic income/negative income tax is some form of "fairness", that taking away the need to work somehow makes people weaker or less moral.

I don't really believe that, but I can't think of any other good arguments against it.

The other argument is that all taxation is theft, and everyone fully earned whatever money he earns in the free economy independent of everything else.

Even if you believed this, basic income seems to be closer to this ideal than the current welfare/subsidy system. I'd be happier paying slightly more in taxes for things which don't create perverse incentives for anyone, but in reality, I think basic income (and a sane defense budget) would be a tax cut, at least after a transition period.