In many places, it is indeed criminal to intentionally expose people to HIV. Problem is, few get tested. Outbreaks, especially with shared needles as an infection vector, happen somewhat frequently.
It's not ignorance, it's sloth and poverty, shame in finding public health clinics or telling a PCP.
There are people that also have (a lot) of casual sex. Or their partner secretly does, infecting them.
Education about partner protection does indeed help right now, but now all will learn the lesson, get motivated, or overcome their fear of admitting the nature of their sex life.
For this reason, the MIT breakthrough offers a lifeline against a disease that is silent, until symptomatic. When it becomes symptomatic, it's already done damage. Becoming poz is unlikely the death sentence it was a decade go, but it's a stigma even if undetectable. At the poz stage, it can't be cleared except under very rare circumstances.
Society does not at this time, tie people down and make them take their meds-- unless they're incarcerated and even then, it's tough. Sex drive is huge. So is drug dependency; you'll get rid of neither.
This breakthrough allows hope. It apologizes for being human, and having a sex drive. Shared needle behavior? No one wants to touch the subject of addiction. Just like they don't want to find ways to herd the unhoused, one individual at a time, back into a functional civil state.