I say neither. The morality argument ignores the reality of decimated gay communities in the 1980s and the ethical minefield of hiding one's HIV status. Furthermore, the medical argument is incomplete. It is true that living with HIV is not what it was in 1985. For one thing, "living with HIV" was a rare and wonderful gift back then. Today, it is a much more common (yet still wonderful) reality. But as long as there is no cure and as long as daily medications will be necessary, an HIV-positive diagnosis is not something to take lightly. It can still kill you.
But, let's not toss the medical argument away entirely. While it may not save all HIV-positive defendants in this situation, there is no reason why every HIV-positive defendant accused of having unprotected sex with an unwitting partner should be treated the same. Here is where the medical advancement argument makes sense today.
We have new and better tests, some of which measure an individual's viral load, which can determine the likelihood that HIV will become AIDS or be transmitted to another person.
The viral load test has allowed us to distinguish one HIV-positive individual from another with even greater specificity. During treatment and monitoring, a high viral load can be anywhere from 5,000 to 30,000 copies/mL, indicated progression of the disease and a high likelihood of transmission. A low viral load is usually between 40 to 500 copies/mL. This result indicates that HIV is not actively reproducing and that the risk of disease progression is low. A viral load result that reads "undetectable" does not mean that you are cured, but it may mean that either the HIV RNA is not present in your blood at the time of testing.
Remember what an aggravated assault was? Attacking someone with the means likely to cause grievous bodily harm or death. It's pretty darn likely that Itchy is going to chop up Scratchy into little pieces when he attacks him with his 1,000 kitchen knives. In fact, Scratchy is going to be really harmed 100% of the time, something the prosecution would be able to prove at trial. (Can you imagine ever bringing Itchy to trial for what he's done to Scratchy?). But, the likelihood that HIV will transmit from one person to another depends on the viral load. A high viral load results in a greater likelihood of transmission; an undetectable viral load means a significantly lower likelihood of transmission. That is important evidence when determining if the prosecution has proven every element of the aggravated assault offense. And, yet, that type of so-called "newfangled science" has not yet been accepted as determinitive of the likelihood element of the aggravated assault offense.
And what about the cause element? Here, defense attornies should be allowed to admit the medical advancement evidence discussed above. HIV is manageable and even if transmitted, it is no longer a death sentence.
Yet, in case after case out of various jurisdictions — including Michigan, Alabama, the United States military and others — proof that the defendant is HIV-positive is evidence enough. As far as the law is concerned, HIV is always active, always transmitting and also deadly. The scientific community knows that is not the case, the thriving HIV-positive community knows that is not the case, and we know that is not the case. And, soon enough, the law will too.
(For those in the biz or just interested in this stuff, watch out for a law review article I will publish on this very topic in the coming months. More info forthcoming.)