OK you've summarized the argument of the Massachusetts SJC. If I accepted their logic, we wouldn't be debating anything. I take the side of the dissents. I believe this gives me a huge advantage, because their arguments make much more sense. The dissent is essentially that
there is a rational basis for allowing the legislature to define marriage as a union of one man and one woman. I expect more from you than just repeating your belief that there is no such rational basis.
Using that definition in law does not create a second-class citizen of someone who:
a. does not want to marry a person of the opposite sex
b. would like to form a union with a person of the same-sex and have the state treat that union exactly as it does marriage.