Kudos to the Iowa Supreme Court for making its oral argument in Varnum v. Brien as user-friendly as possible. Chief Justice Ternus even explained from the bench the steps in the legal process. A number of media outlets streamed the argument live. If it's archived anywhere, it will be through one of the links in the Court's website.
That said, there was nothing new in the argument by the state. In fact in advocating that marriage is by definition between one man and one woman, the state was relying on the argument that won in the early 1970's when the first challenges were brought.
Beyond that, there were the basic right-wing marriage movement arguments: the purpose of marriage is procreation; a man and a woman, even if infertile, represent the essence of marriage; dual gender biological parenting is optimal; a daughter needs a mother to learn how to be a woman and a son needs a father to learn how to be a man. If same-sex couples can marry, then, not tomorrow, but in a generation, people will think it is not necessary for a child to have a biological mother and a biological father and the state will have taught that it is not necessary to get married. When the state allows same-sex marriage it is teaching that marriage is not about procreation and over time that means that more children will be born outside marriage because heterosexuals will not see the link between having children and getting married.
Since we allowed no fault divorce in 1970 we have been trying to put the toothpaste back in the tube (yes that is exactly what he said). It is not desirable for children to be born outside marriage. When parents divorce we have a preference for shared custody because children need to know where they came from, to know who they are. Same-sex couples use artificial means to have children and this deprives children of a biological parent. (One of the justices did point out that heterosexual couples use these means...but we are not talking logic here.)
Dennis Johnson, arguing for the plaintiff couples, did a decent job responding to these arguments. But he also did, well, what the lawyers always do in these cases: he glorified marriage. He said he (as a heterosexual) would feel a loss if the state replaced marriage with civil unions. He invoked McKinley, the 10-year-old daughter of one of the plaintiff couples, whom he said cried when she learned her parents were not married because it made her different.
Somehow the state always says, as it did in the rebuttal here, that the same-sex couples are trying to knock down marriage. So of course the LGBT rights groups have to say they are not. Where does that leave the argument that marriage is not a more valuable family form than others? that our children have been doing fine even though we have not been able to marry? that no child should feel second class because his or her parents aren't married -gay or straight?