Just a few years ago Justice Kennedy ruled the DOMA unconstitutional saying essentially that the federal government had no business defining marriage. Then he did an about face and said that the federal government MUST define marriage.
Kennedy is just a free-form jurist. He gives whatever reasoning he feels he must for the moment, to fit that specific case. When the next phase of the homo agenda comes along he just mutates his argument to fit the new case. He wants what he wants when he wants it and what the Constitution actually says is irrelevant. He knows he is in the position of power.