Elizabeth Pisani : Sex, drugs and HIV — let's get rational

Elizabeth Pisani at TED2010  (transcript)
Sex, drugs and HIV - let’s get rational
Summary
Rationality is being based on or agreeable to reason.
Although the speaker says that let’s get rational in the title, the cause of spreading HIV is that all people thought rationally about HIV. What?  What shall we do?

As a public health nerd, the speaker really works hard to tell people that sharing needle is very dangerous and getting HIV. It means nearly 100  percent.
As a government, they want to clean their cities to win votes thus they don't allow drugs and they send people to jail soon by only carrying needles.   
Those are easy to understand and rational.
People know it well and people who use drugs that are banned also know it well, though, they don't want to go to jail thus they don't have a needle but they share it. They know that sharing it is really dangers, but they don't want to go to jail. For them, it's rational.
However, infection is not stopping.

Next challenge was about sex in this story.
As a public health nerd, the speaker really works hard this time also to tell that people have to use a condom to avoid HIV. It’s understood well and the people in some groups having more sexual partners in shorter spaces of time, in fact, follow it more than others.
As a government, they also cooperate because they help all people who are in those groups and other groups and companies which are especially commercial sex companies to win a vote. People understand those rationally and the rates of condom use in commercial sex are increasing.

However, infection can't stop by a few people who rationally know that people can't get HIV just by having unprotected sex.

In the last, the speaker angrily tells us that the truth is that everyone has a different rationale 💢

Somehow, I really really understand. It's the same as the Japanese problem: decreasing birthrate and aging of the population problems. There are as many different ways of being rational as there are human beings on the planet. It's relationally glory, though, the rational result is distressful, especially, it seems to involve in sex and drugs.

Words in this story
prevalence /adj/  spread out over a large area
dangerous /adj/  danger /noun/
rational /adj/  rationale /noun/