If gays are born that way, then so are pedophiles, and serial rapists, and so on.
If we are to celebrate the gay lifestyle, should we celebrate the other lifestyles too?
Some people hate a 'slippery slope' line of reasoning, but to me it makes sense. The slippery slope says that other lifestyles will also be legalized if the Scotus rules in favor of homosexual marriage. Scalia argued vehemently in that regard in the Scotus' last foray into homosexualism. He was ignored. Time has proven him correct.
So, you are right on the money.