The "poor suckers" in this case are people donating to charity, and the unconditional gifts are, in fact, actually unconditional gifts, specifically set up that way so the effects of them can be studied.
As for UBI specifically...
> It is forcibly taken at gunpoint (though they will ask nicely many times before pulling out the gun).
This is the case with all taxes.
> Also, there can be no "unconditional" giving without "unconditional" taking in a world with finite resources.
This already happens all the time. The money for the military and Medicare has to come from somewhere, after all.