I truly feel that rescue (and many shelters) are full of bleeding hearts. Compassion isn't a bad thing, but many become so blinded by humanizing what they see in front of them that they cannot seperate and make a rational decision regarding what animals can be saved and what ones can't. Not only does that apply to medical conditions, but it also applies to behavioral issues.
I love my dog Mike, he's awesome, but I firmly believe that the shelter he was in was STUPID to not PTS him upon entry. HE HAD A BITE HISTORY FOR EF'S SAKE! Instead they let him rot in a run for over a year, growling and snarling at everyone who passed, yet STILL trying to adopt him out because they believed that every dog deserves a chance. BS. In today's world of extreme pet overpopulation you have to be picky and choosy as far as what dogs get adopted out. If Mike was a dog that came into any of the rescues that I have worked with over the years I wouldn't even have blinked an eye before telling them to euthanize him.
Now with that I'm sure everyone is like "Holy crap, why do you have a dog like that, then?" Well, he is a good dog. He's a good dog with a dominant personality and a lot of baggage. I have him so that I can learn how to rehabilitate dogs, thus making me a better trainer in the longrun. He now greets people with a super wagging tail and kisses. But if this dog was not adopted out to myself, I firmly believe he would have turned into a dangerous dog. He is DIFFICULT and even experienced people have told me that they wouldn't be able to handle him. I'm a one in a million home for this dog (and I can tell you that I will NEVER want another one) and I don't feel that he was safe to adopt out. With a lot of hard work he is turning into a fantastic companion, a friendly dog so yes, dogs can be rehabilitated, but what is the cost of that? Let's see:
Mike was in the shelter for over 1 year because no one wanted a growling dog with a bite history.
In that 1 year I'd say at LEAST 6 other dogs who did not have those issues could have been in that run and adopted out.
Mike now lives with me. I can no longer foster because he takes up too much of my time.
I fostered 5 dogs in the 8 months prior to me taking on Mike, and I've had him for almost 7 months now, so I could have saved 3 dogs who don't have issues if he wasn't here.
Then when you're talking about dogs with medical problems not only are you talking about cost of space, but also monetary costs. With all of the donations going towards one dog with severe mange, or with parvo, or with hip dysplasia, you are taking that money away from vaccinating and speutering tens to hundreds of other dogs!
Rescues and shelters need to look at the bigger picture when deciding who to save. There are too many perfect dogs out there to be letting dogs like Mike take up a run while you continue to push people to adopt him. That is simply stupid. It's a sad reality but while there is pet over population in such severity as we have today, it is not possible to save them all.