The “money quote”:
Our responsibility, however, is to protect constitutional rights of individuals from legislative enactments that have denied those rights, even when the rights have not yet been broadly accepted, were at one time unimagined, or challenge a deeply ingrained practice or law viewed to be impervious to the passage of time. The framers of the Iowa Constitution knew, as did the drafters of the United States Constitution, that “times can blind us to certain truths and later generations can see that laws once thought necessary and proper in fact serve only to oppress,” and as our constitution “endures, persons in every generation can invoke its principles in their own search for greater freedom” and equality.
It is true the marriage statute does not expressly prohibit gay and lesbian persons from marrying; it does, however, require that if they marry, it must be to someone of the opposite sex. Viewed in the complete context of marriage, including intimacy, civil marriage with a person of the opposite sex is as unappealing to a gay or lesbian person as civil marriage with a person of the same sex is to a heterosexual. Thus, the right of a gay or lesbian person under the marriage statute to enter into a civil marriage only with a person of the opposite sex is no right at all. Under such a law, gay or lesbian individuals cannot simultaneously fulfill their deeply felt need for a committed personal relationship, as influenced by their sexual orientation, and gain the civil status and attendant benefits granted by the statute. Instead, a gay or lesbian person can only gain the same rights under the statute as a heterosexual person by negating the very trait that defines gay and lesbian people as a class–their sexual orientation.
There was no dissent.
You can learn more about the justices here.