You might want to approach this thing from a totally different field and tell him you will drop the subject forever if he will go to the humane society every sat for, say 10 weeks where he will look at each and every dog and then the following week he will inquire about those not there and where did they go? Dogs who arent fixed want to make puppies - it's their JOB! They will disobey sometimes when the urge is strong and if you can't guarantee that he can't seize an opportunity to visit the ladies, know that you're taking a risk with or took part in a litter (no doubt adorable little pups), who may find themselves homeless or worse in the future where they might end up in the society he visited. If you're not going to breed him properly, get your dog fixed, it's the killing I can't take - not the sterilizations.
What I want to say to you....will get me banned. So I will approach this differently.
Firstly, yes, dogs create puppies. The whole " omg the poor poor dogs in the shelter are dying because you wont neuter your dog" bullcrap will not work on me. MY dogs never put any of those dogs in the shelter. I used to volunteer at a high kill humane society and not ONCE did I ever feel guilty about keeping any of my dogs intact. Not ONCE. I am currently involved in rescue and am an open foster. Again, I do not feel guilty about keeping dogs intact (cats are a whole different ball game).
My dogs wont breed, my dogs are trained properly. My intact dogs never held the "omg i must breed now" attitude. In fact, my intact Rottweiler NEVER was leashed. Ever!. The only time this was was leashed with a 1 foot tab was in highly busy public areas and trips to the vet. I had him around in heat females frequently at shows, events, competitions and never once did he stray from his heel position.
Its sad seeing dogs in the shelter but they were not put there by my dogs so why should I neuter mine? To prevent the less then 1% chance of my dogs getting loose and fathering a litter? My dogs health comes first.....sorry. Using this guilt tactic does nothing for me and I hope the OP doesnt listen to it. Shes kept this dog intact for a a while with no issues. The issue is not the dog getting lose but the temperament hurdle.
I can fix my dog tomorrow, and I can promise you the shelter numbers will not decrease. It will only decrease when puppy mills, irresponsible owners and BYB's are FORCED to spay/neuter. Those, are the ones that will make a difference in the shelter population.
Seriously, give your head a shake. Vasectomies offer an alternative to neutering which can effect the dogs health short and long term!