If there's a push for a socialist society where the foundations of individual rights and liberties are undermined and everybody is thrown together living collectively off one pot of resources earned by everyone, this is one of the goals they have to go to, same sex marriage, because it has to plow through marriage in order to get to their goal. They want public affirmation, they want access to public funds and resources.
The Hill has more ridiculous assertions from the interview, including King's opinion that "Not only is [same-sex marriage] a radical social idea, it is a purely socialist concept in the final analysis." Matt Corley at Think Progress posted the full transcript, with an audio clip.
King's logic eludes me. Perhaps someone can explain how individual rights are supposedly undermined when same-sex couples gain legal rights already available to heterosexual couples. Maybe King just wants to show that he really is as wingnutty as any Iowa Republican on the subject of gay marriage.
Having spent a fair amount of time in the former Communist bloc, I can assure King that the socialist world was extremely homophobic. Same-sex relationships had no legal status in any communist country, and homosexuality was a crime for decades in many of them.