The measure is direct harm to others. A gay relationship/marriage/whatever deprives no one of anything. Theft deprives the property owner of property. This is a false analogy.

But the truth is that neither of us can make a rational case for his opinion that the other will accept. We've tried persuading each other before, and it passed some time in the days when there was time to pass, but neither of us could effect a change in the other's beliefs around this.