I'm not sure you understand how bad addiction can be. If enough people give an addicted person money, that doesn't mean they'll buy "the drugs they need" and then spend any surplus on things they actually need. They could just as well buy way more drugs than they need and die of an overdose that you helped enable.
People don't overdose because they buy too many drugs. They overdose because they combine drugs they shouldn't (like heroin with barbiturates) or because they buy drugs that have been cut with lethal substances, or because a batch is too strong and although they take the same dose they take usually, they end up taking too much. Or even because they're used to taking cut heroin and they suddendly find some that is unusually pure and take their regular dose and overdose.
