Regardless of what type of sex two people have with each other, monogamy is of utmost importance, and it should be preceeded by lengthy abstinence.
I do not need to reconsider which orifice my wife and I choose that night because there is no chance of any type of STD being contracted.
The rate of AIDS and STDs among "straights" is very high as well. Its not just a gay thing.
While it's not just a gay thing, the rate of AIDS and STDs is extremely high among homosexuals: Health Hazards
PG-13 POST WARNING
The spread of AIDS isn't so much a gay thing as an anal thing. The chances of contracting HIV/AIDS through anal sex are exponentially greater than the chances of contracting it through "normal" sex. If someone, gay or straight, goes around having anal sex with relative strangers, their risk factor for AIDS goes through the roof. It "just so happens" that it's gay men who engage in this sort of behavior more frequently than other groups.