I agree with a few others that have said its a rare defect in the many, many combinations of DNA. Its not a defect in the sense that its a truly negative thing to be, but solely on a purely mechanical look at how sex and the reproduction of the human species occurs.
Same as someone born with extra/less toes or a hair lip. Out of their control and purely a rare and result of the variation in the genetic code.
Now, I don't think that answers 100% of everyone out there as sex feels wonderful and there's bound to be people who are primarily bi-sexual who simply just love the feeling could care less where it comes from. However, I'd bet they have have a specific preference to whom they actually have a true "love connection" with... and that would be based on that genetic sequence.







