If there is no significant chance of untreatable disease, it is not 'irresponsible' to have a very active sex life. The irresponsibility stems purely from the danger. Without it, it becomes a moral issue and is quite different from 'irresponsible'. And yes, there are people who actively oppose any development of an HIV vaccine or cure due to their moral fear that people will start having more sex. The chaplain of the CDC announced in the 1990s that he would do anything in his power to prevent any research into an HIV vaccine, for example.

The most likely significant health threat as far as STDs go in the future are anti-biotic resistant gonorrhea. There were a couple of those spreading in Asia a couple years ago that were positively nightmarish.