There's an old saying about health care that follows along the lines of something like an ounce of prevention equals a pound of cure. That's probably not it exactly but you get the general idea; preventing an illness is a heck of a lot more effective a means of health care than curing it. It only make sense, once somebody gets sick there's no telling what could develop and how serious it could get, so it's best if they never get sick in the first place.
It seems to me that it would make even more sense when it's a disease as fatal as HIV/AIDS. There's no cure for HIV/AIDS, but there are many ways which to prevent the spread of the disease, even among those at the highest risk. Condoms for people who have sex with multiple partners and clean needles for people who inject intravenous drugs isn't a hundred percent guarantee that HIV/AIDS won't be passed from one person to another, but it's a heck of a lot safer than any of the alternatives out there.
What about abstinence you ask? Well sure, if everybody, everywhere in the world, stopped having sex before they were married and only ever screwed one person in their whole life, it would go a long way to preventing the spread of HIV/AIDS. However, I don't know what world you're living, but for the one I live in that's not what I'd call a realistic proposition for even the heterosexual population. In fact according to statistics reported in Elizabeth Pisani's wonderful book on HIV/AIDS The Wisdom Of Whores in North America alone 70% of people who sign abstinence oaths end up having pre-marital sex. As an interesting aside the majority of those people also have unprotected sex, as nobody seems to have bothered educating them about condoms.
So with evidence like that you'd think that it would be a no-brainer for there to be a concentrated effort the world over to ensure that we focus on getting condoms to people in the sex trade or in other high risk groups, and ensure that intravenous drug users are given every opportunity possible to get clean needles. Unfortunately there are people who think that people dying of a horrible disease is less important than forcing everybody live by their moral code. So the Catholic Church, conservative Christians, and fundamentalist Muslims the world over have formed an unholy alliance to ensure that people don't commit the horrible sin of practising something that could be construed as birth control or that we even give the appearance of condoning drug use..