An interesting article, S.H. Ebrahim, M.T. McKenna & J.S. Marks, Sexual Behaviour: Related Adverse Health Burden in the United States, Sexually Transmitted Infections, vol. 81, pp. 38-40 (2005), reports that sexually transmitted diseases were responsible for nearly 30,000 deaths in the U.S. in 1998. A third of the deaths were among women, and two thirds among men. By way of comparison, there were about 44,000 deaths caused by car accidents, a titch over 30,000 suicides, a little under 18,000 homicides, and a bit over 30,000 total firearms deaths (including suicides, homicides, and the few accidents). Three quarters of the deaths were from HIV, but nearly 5000 were from cervical cancer, which seems to be generally caused by some strains of human papilloma virus, and nearly 2000 were caused by sexually transmitted hepatitis and hepatitis-caused liver cancer. (The study purported to take into account the fact that not all hepatitis is sexually transmitted.) There were also over 100 deaths from syphilis and fewer than 10 from gonorrhoea (presumably from the very rare gonorrhoea-caused heart disease), but apparently modern antibiotics have done a great deal to limit death and serious illness caused in the U.S. by bacterial sexually transmitted diseases.
The study also reported that sexually transmitted disease causes some 600,000 cases of infertility per year (overwhelmingly among women); and of course hepatitis, cervical cancer, liver cancer, and HIV can be quite painful and disabling even when they don't cause death.
There are vaccines against hepatitis, and now a promising new one against human papilloma virus, but of course not everyone is vaccinated, or likely to be vaccinated soon. And while condoms can reduce the transmission of viruses, of course people often neglect to use them, or decide not to use them. However much you try to educate people about this, you're highly unlikely to get to anywhere near 100% condom use, even in relatively high-risk encounters.
I disagree on many things with many of the foes of the Sexual Revolution; I don't have moral objections to casual sex or to promiscuity; and I certainly don't support criminalization of consensual adult sexual behavior. Nonetheless, it seems to me that we need to acknowledge that sexually transmitted disease is a serious matter, and there are real medical costs (as well as real hedonic benefits, plus real hedonic costs) to the glamorization of relatively casual and promiscuous sex that seems present in our culture (though not in all of its subcultures).