Today, there are more than 25 different Sexually Transmitted Diseases. In the 1970's there were only 2 significant kinds.
Why such an increase over the last 40 years? The 'safe sex' mentality is partly to blame. Teenagers and adults alike are given a flimsy latex condom and told that they are "protected." In scientific writing the word "protect" can mean anything from somewhat better than nothing to complete safety from a risk factor. Condoms to not take away the risk of contracting an STD, they merely reduce someone's risk.