Easy explanation, though it is always overlooked. The Leftist haters of America know that homosexual is the biggest affront to the conservatism on which our country was founded - even Leftists know at their core that homosexuality is a deadly perversion - and so wield it as as the most reprehensible battering ram against conservatives, who, inherently, are reluctant to talk about such a subject. It's like the horses head left under the covers, to humiliate, horrify, and extort. That is the only value of homosexuality to the Left. And they market it to America for the homos for this very purpose.
There is one more “value” of homosexuals to leftists, “Obama’s Brain,” his former Chief of Staff Rahm Emanuel has described the homosexual voting bloc as “the next Jews” in terms of the amount of campaign donations for Democrats.
http://topconservativenews.com/2013/06/emanuel-proclaimed-that-gays-are-the-next-jews-of-fundraising/