Yes, I am, but that’s incidental. On this specific issue (indeed, any specific issue), one can ask “why do you believe as you do?” If one gets an irrational answer and demonstrates it as such, one can ask again, get another irrational answer, demonstrate it as such, ask again, get another irrational answer…
It is reasonable to conclude after several iterations that a rational answer isn’t coming.
Offhand, I can think of four or five pathways at justifying a ban on gay marriage that have been floated on this board. They all boil down to “gays are different and should be treated different.” A particular favourite of mine is about gays not being able to have children, in determined indifference to straight couples who can’t have (or don’t want) children. For me, the final nail in that coffin was discovering that in at least one state and under certain conditions, a fertile couple can be denied a marriage license. Not only is there no law having fertility as a requirement to legal marriage, there are cases where fertility is a barrier to legal marriage.
That line of discussion usually involves goalpost shifting, trying to define “potential” fertility as a key element (and in determined indifference to artificial insemination and surrogacy, which were developed for infertile straights and which gays can use), then something about the state has an interest in “encouraging” heterosexual reproduction (with no indication of how gay marriage impedes this), and so on.
At some point, it’s perfectly fair to conclude that the fertility issue is a dead end, that anyone using it to justify opposition to gay marriage is not doing so rationally. Subsequently, anyone who starts an argument against gay marriage by citing fertility can be written off by default, thus avoiding the waste of time of going down that path again.
Frankly, if you know of someone who has (or thinks he has) a good reason to oppose gay marriage, tell them to open with it. It’ll save time.