"the only reason HIV transmission is high in poor countries is because, well, they're poor."

This is factually untrue.

Being poor does not equal a HIV transmission rate. There is no 1:1 correlation.

A single protected (condom) sexual act between a male and female averages somewhere around 0.1-0.5% chance of pregnancy, and during the fertile window it could still be around 1% or more even with a condom.

Chance of HIV from one act of unprotected vaginal sex with an HIV-positive partner: ~0.08% male-to-female.

The high HIV transmission rates are NOT correlated with wealth, but social behavior. Unprotected anal sex with many partners? High risk. Now, Africa - the practice of dry sex contributes a ton to HIV transmission. Cultural belief that a dry vagina increases pleasure, hence woman use sand, chalk or bleach to dry out their vaginas, massively increasing HIV risk. Needle sharing of drug users? High HIV risk.

Not a class issue, no reason to punch down on poor people. Poor people have agency and many do not infect themselves with HIV in the first place.

I don't think the original assertion is "punching down" on poor people. While you're correct that poverty isn't the "only reason" for high HIV transmission, poverty certainly contributes to it, via lack of access to health care and lack of access to education. How is it less "punching down" to attribute it to social behavior and culture? Isn't needle sharing associated with poverty, or would you also call that "culture"?

I’ve never heard that before. That explains a lot.