There are two groups of reasons to refrain from promiscuous behavior. One is the high-visibility, high-impact kind of reasons, like risk of infections. The othe

There are two groups of reasons to refrain from promiscuous behavior. One is the high-visibility, high-impact kind of reasons, like risk of infections. The other is the low-visibility, high-impact kind of reasons, like effects on morality, family relationships and whatnot. Now the other group, being low-visibility, is much harder to convince people about, than the high-visibility group of reasons. Whoever teaches people to refrain from promiscuity may be naturally fond on the high-visibility group of reasons as an easy argument. Should the high-visibility group be dismounted (by successful vaccinations, in this case), it suddenly becomes harder to get the message through. Which was expressed in a slightly roundabound way with, ``and by eliminating [[the highly-visible risk]] [[people may feel greenlighted]] for promiscuous behavior''. In short, a vaccine by itself isn't a message in any direction (it's neutral), but lessens one of messages left there by evolution (STDs). Uh, that's my take, anyway.