I have to argue that, respectfully of course.
Properly bred purebreeds have less problems than moggies. Moggies don't benefit from hybrid vigor because they are not mixing species, only mixing breeds. In fact, moggies become susceptable to at least TWICE as many genetic problems as purebreds. A persian/abyssinian cross would not only be genetically predisposed to problems that commonly afflict persians, but ALSO problems that commonly afflict abyssinians. The difference is not as dramatic as it is in dogs, but it is there. Mind, I said PROPERLY bred purebreeds, meaning the genetic testing has been done, and the breeder has done their utmost to care for every need. Backyard breeders, in cats and dogs and any other kind of animal that you can think of, is where the real problem lies.
If no one bred purebreds any more, they would vanish. Forget asthetics, forget 'prestige' (which are both wrong reasons to buy a purebred anything...hundreds of years of selective breeding, of cultural history...down the tubes. Moggies would intermix until all cats looked exactly the same, a dusty brown tabby reminiscent of the Scottish wildcat. Same with dogs. They'd all breed into something that rather resembles a dingo. Purebreeders preserve heritage, culture, and in the case of dogs, functionality. The only breeding in this day and age that can be condoned is the RESPONSIBLE, TESTED, MONITORED, RECORDED breeding of purebred cats.
As for the cat most likely would not have escaped if it had been neutered, I have to wonder what you base that on? Cats are curious. I have six who're all fixed (save one, who is too young yet), and who have been indoor cats more or less their entire lives. If I were to leave for work and leave an unscreened window open, or the sliding door proped, or my front door wide...I would come home to no cats. They would leave, pure and simple. They may not go very FAR, but they would still leave. And be at risk for many possible, horrible fates.
My purebred bengal (my only purebred cat out of a lifetime of owning rescued moggies), is an F3 male, meaning he's 99% likely to be sterile. I still plan to fix him when he's old enough and I feel he's ready for it. If he got out by accident, and I found him two days later with a neighbor who, upon returning him, informed me that she'd had him nuetered, I'd be utterly furious.
NOT because he's a breeding cat, which he isn't (and couldn't be, even if I wanted to do that).
NOT because I had no intentions of not getting him fixed myself, being a responsible owner who cares about the health, temperment, and wellbeing of her pets.
But simply because it was in no way her right to make that choice and put my pet at risk. They don't know the animal's history. They don't know if they have problems handling anesthesia. They don't know its allergies. Or if it has any stress related ailments. They have no right or cause to do so, after two days.
If they had him a month and were actively seeking to find his home, I could forgive that (and probably be exceedingly grateful).
If he somehow found a feral colony and he was 'trapped, neutered, and released', I could most certainly forgive that.
But in these set of circumstances and in this particular scenario, they were utterly, totally, one hundred percent, completely out of line.