Another good point..thank you
In addition to Myron's good idea, it could also be that this is when he feels the most engaged with his wife. Sure, they're arguing, but they are also apparently communicating, and not distracted by other things, and listening (at least enough to fight). This might be better than at other times, since people's lives are busy and harried. I'd also suggest that he has somewhere possibly learned to associate aggression with sexiness.
That is a good point and fits his personality style...thank you!
In my opinion, I think he's getting an erection from argument because he mentally believes it's going to lead to make-up sex.