He's actually very horse-smart. He just doesn't think chopping off a horses nuts is fair when he didn't do anything wrong. It's not the horse's fault that he had bad breeding or faulty trainers. I see what he means, but fair or not, its something that needs to be done.
He's an idiot and if you buy into his thinking......well, let's say you're well suited to each other.
I own stallions and I have a HUGE liability policy to cover me if my horse ever gets out, breeds a mare whose owner didn't want bred, breaks down the fences between me and my neighbors, loses his mind and decides to hurt a human. That policy caused my "escrow" portion of my house payment to go up $400/month. Do you have that kind of money to p*ss away on a stallion, who in your own words is not breeding quality? Or will you just run bare and cross your fingers?
My stallions are easy going, respectful and can be ridden in any crowd and unless someone looks, they'd never know the horse was intact. They are used for breeding, and the second one of them gets out of line, they lose their parts; doesn't matter what I paid for them.
You are already subscribing to the beliefs that a stallion is a wild, fiery beast who can't truly be controlled or handled. If he misbehaves you'll say, "Well, he's a STALLION!" as if that explains everything and he will go on to become a monster until you have to put him down because you can't handle him any longer.
If he's not only breed quality but such an outstanding specimen he takes your breath away, then geld him. You're doing him a favor.
If the boyfriend persists in his thinking, find another boyfriend.