It's been shown over time that no matter how many taboos you put on sex, they are still going to have it if they have a mind to. Fully educating them in protection and best practices is the only way to help prevent STD's and unwanted pregnancies. Abstinence only, give's an alternative, but doesn't actually address the problem.
While abstinence should be encouraged as the only option that guarantees protection from STDs, comprehensive sex education is overall the most effective way to fight STDs such as HIV. No matter how much emphasis is placed on abstinence there will always be those who still choose to have sex. It is important that these people are at least aware of how to best protect themselves.
Comprehensive sex education is the better approach at fighting STDs/HIV. I do not care who you are if you tell your children to be abstinence only then eventually one day they are going to have sex anyways. We need to start teaching children everything that we know about sex so that they can protect themselves.
I believe if society really wants to fight STD's then it is best to offer students a comprehensive sex education while still in school, and preferably by the time they reach 12 years of age. Students start having sex earlier than most parents and adults are willing to admit. If you really want to combat STD's this is probably the only way to do it.
Abstinence-only is a failure in terms of sex education. Kids didn't buy it, pregnancies and sexually transmitted diseases skyrocketed where it was "taught." A complete, utter, dismal failure. Accepting kids are going to have sex no matter what we tell them means we can work a harm reduction approach of telling them the real world consequences of having sex, and what steps they can take to avoid OR minimize them.
The idea that best way to combat the risks associated with sex is to tell people not to have sex is almost comically absurd, if it weren't so detrimental to the US. Sex education - not sanitized or reached by group consensus, but the kind designed by professionals, is the only proper method of teaching young people sex.
If abstinence is taught without comprehensive sex education, there is likely to be an increase in STDs/HIV. How can someone possible protect themselves if they do not know what they are doing. Being told not to have sex is likely to encourage people to do so. It is like telling a child they can't have an alcoholic drink until they are grown up. People always want the forbidden.