Ummm...my response to your husband is pretty simple. Rather than trying to intellectualize this, and look at as depriving an animal of the experiencing of maturing "naturally", you can look at it from the standpoint that what the animal never experiences, the animal will never miss. They simply don't apply philosophy or conceptualization like this to their every day lives...they can't. They're animals. One of the dumbest things we do as humans, is give human characteristics to our pets...it's not fair, and it places intellectual and emotional expectations on the animal that simply cannot exist. It's silly!!!
And, it has nothing to do with convenience. What a load of hoo-ha!!!!!!!!!!
If convenience means protecting your pet from reproductive-related health problems down the road, such as mammory, testicular, uterine, or ovarian cancers, than I guess, yes, I'd say the "convenience" is definitely worth it. If you DON'T love the idea of your pet incessantly reproducing litter after litter, having to find GOOD homes for unwanted puppies and kittens, cleaning up and neutralizing territorial markings, listening to your adult female caterwauling in the middle of the night for a mate, searching for your escape-artist kitty that will do anything and everything in his/her power to make a mad dash outdoors to find a girlfriend/boyfriend, and having the knowledge that for every new kitten and puppy born, another adult shelter animal misses the opportunity to find a loving forever home, then, I'd say the "convenience" of spaying and neutering is worth it. Count me in, folks!!!!
Cats and kittens do NOT mature oddly from being de-sexed. I'd say they mature far more peacefully, as you're removing the turmoil that all of those raging territorial and reproductive hormones throw into the mix. You end up with a calmer, more family-oriented companion, and with a lot less behavior and territorial problems, not to mention you'll be completely eliminating the potential for several reproductive cancers down the road.
Oh, and BTW, the surgical procedures for spaying and neutering are very safe, and relatively low-risk in most cases. Very few animals experience any difficulties during the recovery...it's the anethesia that most vet professionals are concerned with. And NOT spaying and neutering will often mean that the animal will have to be anesthetized in the future to remove a malignant ovarian or testicular tumor, so either way, it's a MINISCULE risk worth taking.