Sorry for the late response. Egads, what a nightmare trying to find a vet who is first experienced with rabbits, and then also as an advocate for neutering.
If you ever plan on getting a buddy for Sable, then it will make it MUCH easier to bond if he's neutered. And if you wait until he is after five years old, then my understanding is it becomes risky. The earlier you get a bunny neutered, the less likely negative habits, like aggression, spraying (IF he does that) will set in.
There is a cancer risk in unaltered males, though MUCH lower than in females.
Altered bunny urine is less smelly. Though it sounds like Sable is litter trained already, so at least the smell should be confined to the box.
Many unaltered bunnies, though not all, display territorial behavior which can cause aggression.
I have had friends who have either got an elder bunny or chose not to have a bunny altered, and seemed fine with it. It really depends on the bunny's behavior, if there is a buddy and the age of a bunny, but obviously it is a decision that only you would have to make. I understand that because of what has happened in the past, that this whole thing may make you uneasy. And I also commend you on still considering it, and forging ahead to find the right vet.
The rabbit community that I am a part of, which includes several rabbit savvy vets, are all advocates of spaying AND neutering, and so a vet who says the surgery is unnecessary is foreign to me personally.
What has been happening with all of this lately?