I don't disagree with your general principle muttynutty, but there are some cold harsh realities to face. For example, a not uncommon progression would be:
Person A "fucks the dog up" - through neglect, through mistreatment, through ignorance, through lack of training, whatever.
Person B takes on dog with best of intentions; inadvertently makes things worse through inexperience of issues/bad advice from so-called expert and struggles to cope; surrenders dog to rescue organisation at end of tether.
Person C rehomes dog from rescue with incomplete knowledge of issues; discovers serious problem e.g. biting. Person C has small child and feels unable to risk child's safety; returns dog to rescue at end of tether.
Rescue try to work with dog but resources are stretched and dog does not respond well to kennel environment. Behaviour escalates; rescue take decision to PTS on behavioural grounds.
Should persons B and C beat themselves up for evermore for trying, just because they didn't have the experience or the resources or, in the case of keeping a child safe, the time to work intensively on the dog's issues? It isn't always as simple as "can't be arsed".
For example, we have a rescue with issues, one of which is separation anxiety. We are working on this along with his other problems and it is improving slowly. Our rental lease says we can only keep pets if they do not cause nuisance to the neighbours. One neighbour has already mentioned that he has heard the dog barking when left alone. We try to keep the occasions when he is left to a minimum but it's for his own good to learn the sky won't fall in if he is, plus it isn't always avoidable - I work full time, my DH has regular medical appointments. I love the dog to bits and we have spent hundreds on vets bills and behaviorists but I will not be made homeless because of him, so if we can't get to the bottom of his problems and the neighbours complain to the landlord in future, the dog would have to go. My disabled DH having a roof over his head is more important than the dog when the chips are down.