Boy Rod, I'd have to totally disagree with you there I'm afraid -- from time spent with dogs and with working with rescue groups. I don't view it as only a convenience for owners to prevent unwanted puppies and the stress of pregnancy -- which is far more stressful on a female body (human or otherwise) than not to be pregnant. Also I have found very few cavaliers lacking the general robustness to not easily weather a basic neuter procedure. I think most dog owners generally do not have the wherewithal to manage unneutered males and unspayed females, heats and marking/roaming etc behaviour... dogs do live a life WITH humans and therefore I do think what owners can manage is a major part of the equation. I know many longtime, experienced breeders whose judgement I would totally trust who would not ever have any issues with a late spay either. I do acknowledge that there are different opinions but the potential complications just of basic pregnancies and lost, roaming male dogs (setting aside all other health issues) that would ensue if cavalier owners followed a general policy of not neutering would to me, be FAR more detrimental to individual dog's health and well-being than SM for example. I feel very strongly about that, and I live in a country where cavaliers are a very common breed and where vets have performed thousands of neuters without detrimental affect. I don;t think US cavaliers are that much more delicate than UK or Irish cavaliers. I don;t know a single vet who would feel cavaliers are to be marked out as being a special exemption to the benefits of spay and neuter.
Here in Ireland (and in the UK) we put down more dogs than can ever be homed and that includes cavaliers and cavalier mixes. I have been told by breed rescue individuals in the US that in some regions, a tipping point has been reached where there are more cavaliers than they can rescue from pounds/shelters. I do not ever think death of unwanted offspring is a reasonable alternative to a spay or neuter of a potential parent, whatever the other considerations.