Besides the fact that gay men have a brain chemistry and brain structure that goes with that behavior indicating it not being a choice or even a learned behavior? How about that many gay men DON'T do that? Many of them engage in alternative sexual behavior they consider more sanitary etc. Those that do have very specific hygenic measures taken to avaid issues. In fact many straight men do the same with their wives, though those women don't have a prostate stimulus that evokes a pleasurable from the expereience.
Also dysfunction has been defined as something that causes a problem with living daily life without psychological stress...the only stress there is caused by people who picket military funerals b/c of them.