LtEveDallas: re locking jaws -sorry, that was my understanding from what was available on bull-type breeds. If its a myth, that's reassuring then.
Re bigger dogs and bigger space - I take your point, of course, but I was thinking of actual space. A big dog in a small home with children and movement, loud sounds etc - some dogs might find that overwhelming and need to be able to retreat from it. In a small space, there are fewer places to go. It was simply logistics.
I am a dog lover. I would love a dog but have a husband who doesn't 'see the point of them' (poor sod never had any pets as a child) and a child who is now terrified of them, thanks to irresponsible owners. Plus we live in a crowded city in a rented flat. So it's not going to happen. However, the more programmes i see on TV about dog rescues, the more I trawl Battersea and other rescue websites, the more I wonder if more dogs shouldn't be just put to sleep immediately, rather than languish in kennels getting stressed (like being in a scary prison for years). Many have been abused or poorly bred. Look at Gumtree. All these badly bred dogs, some now being brought in from abroad because obviously we can't produce enough of our own. Being sold to people who shouldn't buy them because they live in flats, rented accommodation, have small children, want them to assuage their own social inadequacies, or even to use in criminal activities. So, when the novelty wears off or indeed as another poster said, when they can't handle the dog anymore, by some mechanism or another the dog ends up in a pound or rescue centre. Enter responsible potential owner, looking for family pet. And yes, I do know that responsible rescue centres like Battersea rehome responsibly (I had one such dog). However, many dogs are labelled 'no children under 13; no children under 8; no children; looking for an experienced owner who can help X address her possessiveness over food; etc.' And don't forget that even these rescues sometimes get it wrong -dogs are returned to them 'through no fault of her own, X is now back looking for an experienced owner who can help her overcome her abandonment issues'. etc.
Many of these dogs are just problems waiting to happen- because even when rehomed with no children, are they going to live forever in a childless vacuum? I won't bore you with details of owners who insist that their dog won't bite and really likes children, when clearly my child is hyperventilating with fear as the dog leaps up at him, or just won't go away and the owner doesn't seem to think they should call the dog to them. (Not all, obviously and when I had a dog i am ashamed to admit i was one of these owners. Mea culpa.)
But, they are animals, not people, and I think we have to prioritise human need (much as some humans are vile, and some animals are lovely). Some of these dogs have been badly treated. Some of them have been in kennels for long periods, or periods long enough to cause them harm. Plus there are so many unwanted dogs, and more coming on the market. They cannot all be rehomed. Some are not fit ('cannot be rehomed with children.' A dog that can't be near children shouldn't be rehomed - it will come across children one day. It might be your child or mine.) Shouldn't we just accept that the vast majority of these dogs are better off destroyed after 7 days?