One very interesting argument in regards to stopping AIDS: More sex. At least in the Western World.
Consider a 5 person society. Person A wants to engage in sexual activity, but Person B is far too shy to actually have a fling. Person A can then choose between C, D, and E, all of whom are very promiscuous and have already contracted AIDS.
If Person A wants sex, Person A is getting AIDS.
Real societies, of course, are not like this, but consider a typical college population of 100 people, 50 female and 50 male(the female ratio is actually higher, but the difference doesn't matter). Let us assume that, per my personal statistics, half of the females are in relationships, and a quarter of the males.
Thus, we have 25 women and 37 men that are single.
Of these, lets assume that 10 women and 16 men are looking for a purely physical relationship or a hookup at any given time. The rest just don't see the point, are too nervous, etc.
These people are more likely to be promiscous in general, and are more likely to have already contracted an STD. Let's say the rate is 50%, meaning that there are 5 infected women and 6 infected men.
The typical woman faces a 50% chance of having an infected partner, as does the typical male (the percentages change somewhat if bisexuality is introduced). However, what about those shy people? There are 15 single girls and 21 single guys that AREN'T looking for sex. Perhaps that works best for them, but for society as a whole, it's best if they actually increase their sexual activity. If the typical woman, for instance, has 2 different partners every year, she has a 75% chance of sleeping with an infected person. Throw in 10 of the shy guys, who don't have STDS, and the chances fall all the way down to 53%.
My reponse? Utter hogwash. While AIDS itself could be slowed down signficantly, other STDs would be spread more rapidly. I delibatrley chose high numbers in the example to show that even small percentages of people carrying STDs mean high chances of sleeping with someone WITH an STD. In the above example, only 11 people had an STD. In actuality, the ratio is almost twice that, with fully 1 in 4 18-24 year olds having some sort of infection (and many not even knowing it!)
It's an interesting argument, but one that is ridiculous
ADDENDUM: I let this set for a long time, having forgotten about it completely. The balance of evidence, as far as I know, actually works in favor this argument, advanced by Landsburg in More Sex is Safer Sex