The psychology behind it is pretty sound. When you say "I'm going to take an HIV test," people tend to assume you mean "There's a chance I have HIV."
That just leads to fewer people being tested for it, and increased incidence of sexual transmission.
It's kind of similar to the needle sharing programs for heroin users -- they're going to use heroin anyway. That's a given. They're addicted, and they need to be helped. But until we can get around to helping them, we can at least dramatically reduce blood-borne pathogen transmission. Hepatitis and HIV chief among them.
People with HIV are still going to have sex, but getting them to inform themselves on whether they have it or not will lead to safer practices.
Of course, every other LGBT person I've met gets tested regularly, just in case. I suspect with this anecdote that it's people who are afraid of being considered gay, for instance, who are most at risk for transmitting HIV, because HIV is, in some peoples' minds, "the disease that gay people get."
So basically, this should be a good thing. It's one of those things that seem backwards or wrong on the surface, but then when you dig deeper, it all makes sense.