Comment by sterlind

assume you have a population of IV drug users. as a society, would you prefer to spend nothing and see them develop HIV, or to spend some and control the HIV?

you don't have to care about the drug users at all. even if you treat them as pests rather than humans, we frequently vaccinate pests for public health measures. pathogens will spill over to populations you do care about, they'll create a drain on the healthcare system, they'll harbor other opportunistic infections. it's not sanitary.

this is completely leaving aside that some drug addicts can and do turn their life around, and that HIV is a horrible illness nobody should have to deal with, even if it's "their fault."