Prescription drugs are a necessity for full medical treatment

It should be the government's responsibility to absorb the risk of taking care of its citizens' health. That 'risk' should not be individualized and privatized; that creates misery and suffering.
Furthermore, having completely free and accessible prescription drugs makes certain people more likely to seek treatment for a condition they have (which is socially beneficial) because it reduces stigma and shame which is likely to be amplified when having that extra interaction with a private insurer or financial exchange.