It would be an odd utility function which had an explicit term for gay marriage specifically. Arguments for it tend to be based on broader principles, like fairness and the fact of its non-harmfulness to others.
An irrational opposition might be something like having a term for fairness but failing to evaluate that term in some particular case, or becoming convinced of harmfulness despite the absence of evidence for such.
It would be an odd utility function which had an explicit term for gay marriage specifically. Arguments for it tend to be based on broader principles, like fairness and the fact of its non-harmfulness to others.
An irrational opposition might be something like having a term for fairness but failing to evaluate that term in some particular case, or becoming convinced of harmfulness despite the absence of evidence for such.