He's for the Two Johns for one reason: they are pro-homosexual marriage.
Period.
In Kerry's case, of course, he is pro-gay-"marriage", but it must be pointed out that he has once again done some insincere pandering to both sides of the issue by in theory coming out against gay "marriage" while not being willing to do anything about it in practice.
Ding ding ding! We have a winnuh!