Well, a judge actually. The most popular reading during gay wedding ceremonies is part of the ruling which legalized gay marriage in Massachusetts (the first state to have legal gay marriage). It was written by Judge Margaret Marshall from the State Supreme Judicial Court. While this is by no means the whole ruling, the passage below is the long version and is often excerpted into smaller chunks:
"Marriage is a vital social institution. The exclusive commitment of two individuals to each other nurtures love and mutual support; it brings stability to our society. For those who choose to marry, and for their children, marriage provides an abundance of legal, financial, and social benefits. In return it imposes weighty legal, financial, and social obligations....Without question, civil marriage enhances the "welfare of the community." It is a "social institution of the highest importance." ...
Marriage also bestows enormous private and social advantages on those who choose to marry. Civil marriage is at once a deeply personal commitment to another human being and a highly public celebration of the ideals of mutuality, companionship, intimacy, fidelity, and family.... Because it fulfils yearnings for security, safe haven, and connection that express our common humanity, civil marriage is an esteemed institution, and the decision whether and whom to marry is among life's momentous acts of self-definition."
I hope you consider including a piece of history in your wedding ceremony.
Have you written your wedding ceremony yet or are you using a script provided by your officiant?