> Even if 50% of recipients go buy drugs with the money, does it really matter?
The libertarian dream, however the unfortunate reality is that where the money is supposed to do things like feed your children, you instead squander it on drugs. If the presumption of drugs is too harsh, replace it with something equally stupid like cigarettes, lottery tickets, rent-to-own furniture or some other predatory service that the poor disproportionately participate in. This is not a behavior beneficial to anybody or worth enabling.
This is why we have systems like food stamps (disbursements that can only be spent on food), WIC (disbursements that can only be spent on fresh vegetables, baby food/formula, etc) and so on. Handing cash to people who don't know how to use it responsibly does not spontaneously teach them otherwise.