How, then, did the ban actually work for those people who no one knew had AIDS? Think about it.
I've never even heard stories of people maliciously spreading AIDS deliberately, so unless the US is a nightmare planet, I'm going to make the assumption that most cases are contracted from people who haven't been diagnosed with it yet. You know, the same people who would slip through the net of any AIDS travel ban.
People who haven't been diagnosed with it yet have still contracted AIDS,
therefore, making them careless and neglectful in the first place. I know that there are cases in which someone has been completely careful and has still contracted AIDS by accident (broken condom, false negative test, etc), but there are A LOT of stupid, selfish and neglectful people in the world - plenty of which aren't smart enough to take proper precaution to prevent the contraction/spreading of the AIDS virus.
And, I'm surprised that you've never heard of someone maliciously spreading AIDS with deliberation. There are plenty of cases,
especially here in the US, in which an infected male has purposely raped a woman (more than likely an ex-girlfriend) in order to "get back at them", so to speak.
Also, here is something to think about...
According to the CDC, there are between 500,000-1,000,000 people living with AIDS in the United States. Why is that number so vague? If there was an easy way to detect and keep track of AIDS infected people, then the number would be more accurate, don't you think? That number is so vague because AIDS is often detected only after it's too late, AKA - after the virus has become fatal, allowing plenty of time for it to be passed along to other people through sex, via careless sexual encounters.
There are also an estimated 40,000 NEW cases of HIV/AIDS that are reported every year in the United States.
40,000 NEW cases of HIV/AIDS each and every year...that doesn't sound to careful to me. I know that AIDS isn't on the forefront of the medical community's mind anymore (as cancer has taken control of everyone's sympathy), but AIDS is still an extremely nasty son of a bitch that people have absolutely no respect for.
http://www.avert.org/usa-statistics.htm