Getting beyond definitions, point out that society scorns smoking. Why! Because it's a health hazard. The average smoker loses 5 years of lifetime from the activity. Homosexuality is a worse health hazard. The average male homosexual loses more than 25 years of lifetime from his unique activities. If every male homosexual gave up peter puffing for cigarette puffing we'd see an improvement in public health on an epidemic scale.
The bottom line is that the public endorsement of homosexual relationships may be beneficial in the long run. When lemming populations grow out of control, the lemmings run into the sea in swarms. When human populations grow out of control, humans opt not to breed, abort their progeny, and abuse their progeny. Think about it--it's liberals who are chosing these options. Natural selection in action.