I agree with Young Native that condemning people who express a fetish isn't going to help anything, but to be as honest about my own feelings as you are about yours, OP, I find the idea of purposefully watching people transmit HIV about as appealing as I find the idea of pedophilia. Though there are a great many fetishes I find distasteful, I will argue for them as long as everyone consents and no one is permanently harmed in the process. This, however, falls well below that mark. I am unable and unwilling to hide my disgust.
What's the difference between my opinion and watching unprotected sex?
Unprotected sex can, and routinely does, happen without transmitting HIV. It's a pretty major difference, to be honest. There are all kinds of people out there - men, women, and everyone in between and aside - who have partners whom they can trust to not have STIs. Be it through monogamy, or a carefully-controlled open relationship, there are safe ways to be able to doff the condom and have sex that is as safe and beautiful as with a condom. Watching that is 100% different from watching people kill each other. Even bareback porn - both gay and straight - is made with the assumption that all parties are tested and negative. Regardless of the scruples of supporting those films, they are not produced with the intention of being porn snuff movies. Purposely watching people infect each other with HIV or other STIs? That's a different animal entirely.