Being a homo is a choice.Therapy can't stop someone from being gay, just like it can't make someone stop being straight. It is genetic, and something that is not a choice. You ask why it hasn't "bred" out of humans if homosexuals don't propagate the species? Because it's a minor defect, not an abnormality passed from parent to child. Your question is the same as asking why infertility hasn't been bred out if they can't propagate?
A perverted choice.
But still a choice.