In the case of the HIV-infected homeless drug addict, any doctor can tell you that all of the various things involved have served to compromise his immune system. The HIV/AIDS have just made an already bad situation even worse.
As a counterexample, look at someone like Magic Johnson who is HIV+, but lives a lifestyle of diet, medication and exercise that allows him to keep the disease in check more or less indefinitely. He's the flipside of the drug-addicted homeless person who is HIV+
To figure out the effect of HIV infection, you compare one group of drug addicts who are not HIV positive with a similar group of drug addicts who are, then look at the relative rate of diseases arising from compromised immune systems. You'll find instances of such diseases in both groups, but the rate for the HIV infected drug addicts will be, over the long-term, significantly higher.
You are quite correct that living a life of drug abuse and promiscuous homosexual orgies (with all of the attendant STDs and other health issues) is bad for one's immune system. But that lifestyle, even if it leads to getting certain AIDS-like diseases, is not the cause of AIDS. It can simply lead to health situations that are similar to AIDS, however.
==As a counterexample, look at someone like Magic Johnson who is HIV+, but lives a lifestyle of diet, medication
Last I heard, Magic Johnson discontinued his AIDS chemotherapy drugs over a decade ago.
==You are quite correct that living a life of drug abuse and promiscuous homosexual orgies (with all of the attendant STDs and other health issues) is bad for one’s immune system. But that lifestyle, even if it leads to getting certain AIDS-like diseases, is not the cause of AIDS. It can simply lead to health situations that are similar to AIDS
Again, at this stage of the game, scientists can’t tell the difference. Moreover, the AIDS establishment has put the kibash on all attempts by scientists to resolve the issue. And if they can’t tell the difference, then they can’t be sure what’s really causing AIDS.