I don't think you truly understand my stand, or the Islamic stand, on promiscuity, marriage and homosexuality. Let me explain, as I have done before...
First off, the Islamic Concept:
Men can only marry and have conjugal relations with women. They are not allowed to intermingle freely, as this can lead to pre-marital complications. They are advised to be chaste before marriage, keep their eyes bowed in front of the opposite sex, and generally try not be tempted to commit adultery or fornication. That's it in a nutshell. Now...
Islam's View on Current Affairs of Sexuality
In Western society, Islam condemns ANY KIND of pre-marital relationship with someone of the opposite sex that is based on sexual attraction.
In many societies these days, people routinely have sex outside of marriage, meaning before marriage, with any number of boy/girlfriends. This, in the eyes of Islam, is promiscuity, regardless of whether it is hetero or homosexual in nature. As you can well imagine, having multiple partners increases the chance of contracting STD's and AIDS, as most people do have over their lifetime. So, your view of married couples getting STD's is still from this concept of having partners before marriage; promiscuity in the eyes of Islam. In Islam, this problem does not arise, as premarital sexual relations, even close relations b/w members of the opposite sex who are strangers, is very heavily discouraged and taught against.
The Cure to AIDS and STD's Islam Proposes
Now, this is a sensitive topic. If every newborn or virgin person were to suddenly practice the Islamic concept of relationships b/w men and women, these people would never have to worry about STD's and AIDS if they only married each other. The ideal, or close to it, Islamic solution. the spread of STD's and AIDS would drop very significantly. But that only covers virgins.
About those already infected, this is where I say that more research has to be done. If these people also followed Islamic Law, and settled down, no adultery, no fornication, the level of new infections would also significantly drop. In the meantime, we would focus on a cure for their ailments.
And you don't seem to understand my point. Even if you are a virgin when you get married you can still have or get an STD by getting it from your parents, dirty needles, botched blood transfussion... it's less likely but you can still get it. I believe with AIDS there's about a 50% chance of an infected person passing it on to their child(though I'd have to look it up to be sure). If everyone got married before having sex and remained faithful to their partner then those who had an STD would still pass it on to their partner and it could likely be passed on to any children they had. In fact it is highly likely that the STD would evolve to make itself more likely to be transmitted between mother and child. So marriage might slow the disease down but it would not stop it.