Okay, don't ask me about the science, but SOMEHOW, mid-80s, AIDS morphs into a disease that can be spread more easily than in OTL. Maybe not via mosquito bites(which was in fact one of the many underground rumours in OTL), but perhaps with the same degree of casualness that tuberculosis can spread. Not something you're likely to get from any random stranger on the street, but the news is still alarming enough to engender mass panic.
There are calls for the mass suspension of civil-liberties, in order to faciliate the lock-up of all infected persons. Reagan, who still maintains a schoolboy's civics-class respect for basic liberty, balks at the proposal, as does GHW Bush, but their opinions are drowned out by a doubly energized Religious Right, who now have added credibility with the public, as their previous Doomsday claims appear to be coming true.
So, Reagan and Bush are either pushed out of office, or agree to save their political hides by letting the panic-mongers call the shots. A sort of medical Homeland Security Act is passed, mandating the incarceration of all HIV carriers, along with the deportation of all non-citizen Haitians. A panel, co-chaired by one of the more panicky scientists(for medical legitimacy) and Robert Bork(to provide legal cover) is charged with implementing the new statute's provisions.
These measures provoke the formation of a far more militant version of ACT UP than we saw in OTL, which responds to the state's repression with Weather Underground-style violence, directed against the new medical-sercurity apparatus(quarantine camps under construction are bombed, as are the offices of medical professors who support the government's position). Combined with the already-existing panic about the disease itself, this provides further impetus for the assault of civil-liberties.
Enforcement of state "sodomy" laws comes back with a vengeance(that such enforcement is rather pointless given that the disease is now airborne makes little difference to already homophobic elements of the public), and is met with militant pushback by gay activists. There are dozens of Stonewalls across the land every month.
Meanwhile, rumours persist that the disease CAN be spread by mosquitoes, and enterprising chemical companies are quite happy to promote this idea. Industry lobbyists push for a massive spraying program. This prompts the formation of armed militant factions within Greenpeace and the Sierra Club, who do battle with government and industry.
Not sure how all this ends up. Possibly, the public buys the idea that the repression was neccessary, because it's hard to prove that the less-than-predicted death-toll wasn't a result of the medical-security laws.
Scenarios may vary for other countries, though probably a bit of overlap everywhere.