Did you actually listen to what Mr. Kerry say? I am just playing it on my machine, http://www.npr.org/rundowns/rundown.php?prgId=2&prgDate=current and he is saying that he supports equal rights for homosexuals, including the right to civil unions. He also said that marriage is a religious institution, sanctioned by church, and there should be a separation between church and state. He also commented that he voted against the Defense of Marriage Act because it was gay bashing.
That looks like a very sensible position to me. The state should guarantee civil rights, including those to enter various forms relationships and partnerships, but that has nothing to do with the spiritual or religious dimensions people may add to those relationships. Federally guaranteed right to a marriage" is no different than, say a federally guaranteed right to circumcision or the first communion or a federally guaranteed place in heaven.
Wojtek