Reminds me of the time we fostered a 10 year old, HIGHLY AGGRESSIVE, totally blind, mostly deaf, chow mix with (badly healed) previously broken hips.
She has been an outdoor dog her entire life with 0 socialization, got out the yard one day, was hit by a car and sent to a shelter later. This rescue group picked her up and dropped her off with us to foster. We had 4 other dogs at the time and she had to be given her own room because she would snap and growl at anything she heard in her vicinity since she couldn't see it.
We had her for three days. Three days of this dog living in constant fear because she doesn't know where she is or who is near her, three days of her pissing and shitting all over herself because she couldn't squat because of her horrible hips, three days of agony for this poor dog.
My mom felt so bad for this poor thing, she paid the $500 adoption fee from the rescue group and this chow was legally ours. The next day my mother had her euthanized after taking her to a vet check. The vet said there was no hope this dog would live a happy and normal life with her issues, not to mention she was insanely old and had horrible arthritis and would pass soon anyways.
So after dropping $800 in adoption fees and vet fees, after giving this dog some relief, my mom was publicly executed on Facebook by the rescue group and all its allies. My mom was called a murderer and had everyone yelling at her saying that she "only killed the dog because it was inconvenient to care for". My mom cried for 2 weeks over euthanizing that dog. She wanted to save her, thats why she agreed to foster this unmanageable dog, and when she realized this dog was actively suffering, she spent HER OWN MONEY to end its pain. It killed her to put that dog down. Yet she was treated like a monster for doing the most humane thing.
My mom no longer fosters dogs since she has toddlers and a full time job, but she still makes weekly drives to transport dogs to new homes/rescue groups. Sometimes these drives are 8 hours round trip. She does it all on her days off because she truly loves dogs and wants each and every one to find a home and she does it all for free.
Not every dog can or should be saved. With all the money spent on one unadoptable dog, we easily could have saved 3 or 4 totally adoptable ones. Rescue groups need to focus on saving what they can, rather than trying to save every dog on Earth and causing more to suffer in the process.