Another consequence that not many people think about of dumping pets is that those who do survive often breed with other wild dogs, and dingoes, and become a menace to wildlife and livestock. Where I grew up, this was a huge problem. One farmer down the road from us lost all but 4 out of the 120 goats he started with, in 2 years. All taken by wild dogs/dingo crosses. One year old steers were being taken down by the same dogs.
But I can't imagine dumping a pet. I just couldn't do it. We really want to get a dog (DD loves them) but we just won't take that step until we buy a place of our own, so that we can guarantee it the secure yard space that it needs. We'll also be careful about the size and type of dog that we buy, to make sure it's going to be suited to suburban living. And we're going to get one from the RSPCA. Can't stand pet stores selling dogs and cats, as I know from experience that they are not terribly discerning, for the most part, about the kind of animals that they sell. For instance, selling large guard dogs that will instinctually bark at anything and bail strangers up at the gate, to people living in the suburbs (like the dogs that we used to breed, to protect our livestock from the abovementioned wild dogs) is the height of irresponsibility. Yet every so often I come across a pet store in the middle of Brisbane selling the exact same breed (it's always the same chain of pet store too - I never buy any pet supplies from them on principle). When I do, I let my mother know, and she lets her breeders network know, and they all phone up the store and let them know exactly what they think of it all! We just know that those dogs will either end up being dumped, or debarked, or punished for doing what comes naturally to them - exhibiting guard dog behaviour! So sad.
And then the stories you hear even of people who have pet birds, get sick of caring for them, and just let them go one day, thinking they will be able to fend for themselves. Most of them will not survive the first 24 hours out of their cage.
Yes, sometimes there are legitimate reasons for not being able to keep your pets anymore. But more people need to think a bit more before they get a pet in the first place.