Sexually transmitted diseases in homosexual men.
This is an excellent article written by Handsfield that addresses some of the issues.
He says, "
Gay men appear to be at greater risk than heterosexual men or women for gonorrhea, syphilis, anorectal venereal warts, and perhaps for genital and anorectal herpes simplex virus infection, we well as for several STDs outside the traditional sphere of venereology, including hepatitis A, hepatitis B, amebiasis, giardiasis, shigellosis, enteritis due to
Campylobacter fetus, genital and anorectal meningococcal infection, and cytomegalovirus infection."
He then goes on to say, "Most studies to date, however, have been conducted in STD clinics or at sites where persons congregate for anonymous sexual activity, such as steam baths, and
the applicability of their findings to the homosexual male population at large is unknown."
Here he clearly points out the flaw in those studies as not an accurate representation of the whole homosexual male population, as you have extrapulated yourself. But, he continues and addresses this problem:
"Darrow and his colleagues.. have attempted to address this problem by reporting the frequencies of several STDs relative to various risk factors in a large population of gay men in the general population. Critics will point out, and the authors acknowledge, that the results cannot be considered applicable to all homosexual men; the population sample included only 4,212 respondents (1.5 %

to 275,000 questionnaires published in a gay-oriented magazine or distributed through organizations relating to homosexual men. This study commands attention, however, because of the size of the population surveyed and because it was not conducted in an STD clinic.
The fact that only 36% of the respondents who had sought profressional care for STDs had done so at public clinics supports the concept that this population sample is different, and presumably broader, than other populations of gay men studied to date."
After Handfield addressed the validity of his findings, he goes on to express them:
"The results contain no surprises, except that perhaps that full
78% of respondents had experienced at least one episode of the STDs surveyed; and 2,228 of 3,696 who answered the question fully had experienced an STD aside from pediculosis. Although individuals who had been infected might have been more likely than other gay men to participate in the survey, this probably was
not a major determinant, since only four of the 692 questions directly referred to STDs or to medical issues."
He came up with approximately the same result as the one that was under challenge:
"The infections surveyed occured with roughly the
same relative frequencies that have been observed among gay clientele of STD clinics or steam baths."