Heterosexually transmitted AIDS was a myth created by gays to elicit support for funding.
It happens, but it's very rare.
Through 2007, about 175,000 AIDS cases in the US were heterosexually transmitted. That’s about 20% of the total. Internationally, the percentage of cases with heterosexual transmission is much higher. I’m not sure “rarely” is quite the right word.
Of course I.V. drug users transmit it when they share their needles, but you are correct. Heterosexual AIDS is a myth.
Much like the queers, Africa realized that it could get on the AIDS bandwagon, by classifying everything from Malaria to Pregnancy as AIDS.